The Islamic ideology derives from the Qur’an and Sunnah. Legislation in Islam also derived from these two sources. Therefore if any one of these sources is lost or distorted then the risk is to the ideology as a whole. In this respect the study of Isnad is not a peripheral discipline in Islam but fundamental to the preservation of the ideology itself. Without Isnad the Sunnah as a source of ahkam would cease to exist. Without Isnad we would lose the ability to elaborate, specify and restrict the ambivalent, general and absolute import of the Quranic text since the role of the Sunnah is to clarify the Qur’an. Without Isnad, extraction of Sharee’ah rules for new realities from the Sunnah would cease to exist. Without Isnad foreign elements could have been incorporated within the ideology due to their false attribution to the Prophet (saw). Thus, Isnad is crucial for the purity, clarity and crystallization of the Islamic ideology and its ability to solve new problems from its legislative source. That is why ‘Abdullah b. Mubarak the teacher of Imam al-Bukhari (Rahmatullahi ‘alayhim) did not exaggerate when he said:
"The isnad is part of the Deen: had it not been for the isnad, whoever wished to would have said whatever he liked.’
It is also precisely for this reason that the Orientalists, have sought to create doubt in the efficacy of the Isnad. The wholesale rejection of hadith as a historical source was first argued by an Orientalist named Ignaz Goldziher in volume 2 of his book: Muslim Studiess. Goldziger was then followed by Joseph Schact who developed his ideas and tried to present a substantial body of proof to this effect in his work: ‘The origins of Muhammadan jurisprudenc’ which was published in 1950. And more recently Gautier Juynboll in his, Muslim Tradition. Studies in chronology, provenance and authorship of early hadith’ has developed further techniques to prove the false nature of the hadith literature. The general thrust of orientalism since Goldziher has tended to impute doubt, in various degrees, on the corpus of hadith literature. For them the elaborate isnad which the Muslims adduce as proof of authenticity have either been doctored or embellished such that the hadith literature is more a reflection of the time in which they were fabricated, ie the political and sectarian milieu of the 2nd and 3rd centuries, than the time they are supposed to go back to which is the time of the Prophet and his noble companions. This is one of the more serious and fundamental attacks by Orientalists on the Islamic ideology. Buy throwing doubt on these sources it would be possible to demolish the whole edifice which rests upon them. It was in this vein that attempts were made to discredit the historicity of the hadith literature.
In addition we see the influence of this thought on modernism and modernist thinking where Sunnah as a source of legislation is markedly absent in the political field. Hence we see amongst some Muslims an attitude which considers the Sunnah of lesser importance than the Qur’an simply because the hadith requires further study and scrutiny as compared to the Qur’an. This has led to people either disregarding or neglecting ahkam simply because it is not found explicitly in the Qur’an. Hadiths discussing the unity of the Muslims, the obligation to appoint a Khaleefah, or the ruling that a woman cannot be ruler to name but a few are brushed aside or not given their due weight because they are ‘hadith’ and not an ayah of the Qur’an.
Dr Asghar Ali Engineer in his book The Islamic State says: ‘There is no fixed concept of an Islamic state – much less a divinely ordained one to be treated immutable. The Koran, as pointed out, elucidates a concept of society, not of a state. The theory of Islamic state, as we have seen in the preceding chapters, changed and conformed more to the concrete situations than to any a priori concept.’ The hadiths discussing the Khilafah were fabricated by the rulers to justify their rule. He says: ‘In the metamorphosed state set-up there was nothing more Islamic than the fact that the ruler professed Islam and enforced certain provisions of the Sharee’ah in personal and criminal matters. It was the result of such circumstances that a number of traditions were coined justifying any regime which did as little as enforcing the Islamic way of prayer.’ He then proceeds to quote the rigorously authenticated hadith in Sahih Muslim as example of such fabrication. The text of that hadith is: ‘In the near future there will be Amirs and you will like their good deeds and dislike their bad deeds. One who sees through their bad deeds (and tries to prevent their repetition by his hand or through his speech), is absolved from blame, but one who hates their bad deeds (in the heart of his heart, being unable to prevent their recurrence by his hand or his tongue), is (also) safe (so far as God"s wrath is concerned). But one who approves of their bad deeds and imitates them is spiritually ruined. People asked (the Prophet): Shouldn't we fight against them? He replied: No, as long as they say their prayers.’ This is exactly the view held by Goldziher who claimed that the political hadith literature was a product of the political and sectarian background of the Umayyad caliphate. Recently Dr Engineer gave a presentation in which he sought to prove gender equality and his approach was solely his own personal interpretation of the Qur’an without any recourse to the Hadith. His reason for this is that hadith was recorded a hundred years after the event, they are contradictory or contradict his own reading of the Qur’an and therefore not a reliable source for Tafseer of the Qur’an.
This attitude is dangerous as it is tantamount to disregarding the revelation of Allah (swt) and the reason for this reverts back to the pragmatic view of the Sharee’ah and a sense that Hadith is somehow of lesser worth due to the difficulties posed in establishing its authenticity.
Therefore the aim of this shahriyyah is to establish the firm conviction in Sunnah as a source of legislation by demonstrating the sophistication and success of the hadith methodology in preserving the Sunnah. However, the way I will be discussing this topic is not to present it as discipline of Musatalah al-Hadith as has been traditionally done but to take relevant aspects of the discipline to give us an outline and conception of the methodology and system itself. As for a detailed refutation of Orientalist arguments and proofs, this will not be possible here due to lack of time but it is thoroughly dealt with in my forthcoming work: ‘The Role of Isnad in the Preservation of the Islamic Civilization’
Historical background and the Birth of Isnad
But before we discuss the key aspects of the hadith methodology I wish to recount the historical background of Isnad so that we can appreciate the context in which the Isnad was born and the problems and challenges Muslims faced in protecting the ideology from the pernicious activities of fabricators.
If we start with the time of the Messenger (saw) we find that questions of authenticity was not an issue since the Prophet was amongst them and the Sahabah were able to correct each other if any mistakes were made in narration. So for example ‘Umar once narrated that the Messenger (saw) said: ‘The deceased is punished due to the weeping of his family’ but ‘Aisha corrected him by saying: ‘The Prophet (saw) said this regarding a Jewess that she was punished whilst her family were crying for her’ meaning that she was punished due to dying upon kufr while the family wept and not because the family was weeping for her. At this time Isnad was at its rudimentary stage because of the proximity to the Prophet (saw) but this did not stop the Sahabah from checking strange attributions or corroborating reports when in doubt.
The earliest record of fabrication of hadith started after the first civil war between Ali and Mu’awiya from 35 A.H following the murder of Uthman. According to Ibn Sirin who died in the year 110 AH: ‘They did not ask about the Isnad but when civil war (fitna) arose they said: Name to us your men; those who belong to Ahl al-Sunnah, their traditions were accepted and those who were innovators their traditions were neglected.’ After this time the fabrications increased with varying motivations. Initially the false attributions reflected political differences. According to Ibn Abi al-Hadid: ‘Lies were introduced in Hadith on merits originally by Shi’a. They in the beginning fabricated many hadith in favor of their man motivated by enmity towards their opponents. When Bakriyya (ie supporters of Abu Bakr) found out what the Shi’a had done they fabricated on their part hadith in favour of their man.’
Disagreements in ‘Aqaa`id also led the unscrupulous to fabricate hadith in support of their sectarian positions. So there are one set of narrations which say that the Prophet (saw) said that Imaan increases and decrease wile another set say Iman does not increase or decrease and all of them are fabricated.
Another faction which fabricated hadith were the Zindeeqs ie people who outwardly manifested Islam but hated it and wanted to destroy it being giving an ridiculous and irrational impression of Islam through their fabrications.
Some fabricated hadith to support the founder of their own school like the report which says: ‘There will be among my Ummah a man named Abu Haneefah who will be the Suraj (light) of my Ummah.’ Or the the fabrication referring to ash-shafi’I which says: ‘There will be among my Ummah a man named Muhammad b. Idrees who will be more harmful to my Ummah than Iblees.’ Other categories of people who fabricated hadith were well intentioned pious people who wanted encourage Ta’aat or the story tellers (Qussas) who wanted to entertain the people with their wild and amazing stories.
The Challenges faced by the Muslims:
Revival is intellectual elevation. When society is elevated in thoughts it looks at problems in an enlightened manner and derives solutions on an enlightened basis directed by its viewpoint about life and hence that society progresses and solves its problems effectively and thereby achieves revival. One of the best examples of revival or elevation in thought is the way Muslims dealt with the problem of hadith authenticity and fabrication. From the brief account of history given above the enormous task faced by the Muslims is clear. There were thousands of transmitters scattered throughout the Islamic lands and even greater number of reports to sift through. From these they managed to select the sound narrations from the weak and compile them along with their chain of transmitters in such an effective manner which is unparalleled by any form of historiography known at the time and beyond. And this was done in the days when the best form of data storage was the human memory or parchment and messengers on horses were the quickest form of communication.
To appreciate how tall an order this was let us look at the difficulties the Muslims had to resolve in order to safeguard the hadith. The first hurdle to overcome was to establish continuity of the chain i.e. that there were no gaps in the chain. This required that the birth and death dates of narrators had to be catalogued as well as the cities form which they came in order to establish the possibility that they had met and hence were able to transmit the hadith. Second issue that had to be ascertained was the probity and mendacity of transmitters. It is not enough to have an unbroken continues chain if one of the transmitters is of unsound character. Like a chain all that is necessary for the whole thing to collapse is one wobbly chink which would allow it to fall apart easily. So one liar in the chain, or the weakest link, will weaken the report even if the rest of the chain is littered with illustrious and trustworthy personalities. In fact it was the names of illustrious and respected people that were used by fabricators to pass off their dishonest material. For this reason the Muslims needed to gather information about the narrators, which if one thinks about it is not an easy accomplishment, since it involved assessing the character and state of mind of thousands upon thousands of transmitters. This repository of biographical material then would be used to identify each and every transmitter in the chain. Now having amassed this information there needs to be some criteria as to what would constitute a reliable narrator whose report could be believed. So is it enough for the narrator to be trustworthy before we take his report or should we impose extra safeguards? What about memory? Some people are trustworthy but prone to forget or make significant mistakes or get their reports muddled up. How do we deal with these problems? Also, as we know usually always there is more than one chain for a single hadith, how can we classify these to indicate the various levels of strength and authenticity since the Sharee’ah has imposed diffract criteria in respect to actions and belief? As with all human dependencies mistake will be made so how can we avert mistakes and maintain accuracy in transmission? What about the ostensibly sincere fabricators of hadith who are of sound memory but concoct reports for what they believe to be well intentioned and noble aims? How do we catch them out? What kind of techniques and approaches can be developed to detect forgery and deception? And finally, at times we find two reports both of which are authentic according to the stringent criteria laid out but they contain an apparent contradiction. This is not surprising when you are dealing with reports describing sayings and actions taking place in diverse circumstances in their generic and specific contexts spanning the prophetic lifetime of the Messenger (saw). Coupled with this is the possibility of a mistake that has gone undetected due to forgetfulness or misunderstanding the intent of a statement or action. How do we reconcile such seeming and apparent contradictions? Since the Wahy, as we know, in principle does not contradict itself.
These are just a glimpse of the key issues the Muslims had to answer if the Sunnah was to be protected from loss and corruption from foreign elements. The result was the development of 4 distinct sciences to combat fabrication, namely:
1. ‘ilm tareekh rowaah, which dealt with the crucial issue of the dates of birth and death of transmitters.
2. ‘ilm jarh wat ta’deel, consisting of the manners of disqualification and authentication of transmitters.
3. ilm ghareeb al-hadith, which is study of the irregular aspects of matn and Isnad.
4. ‘ilm mukhtalafil hadith, which discusses the techniques of reconciling and outweighing seemingly contradictory hadith.
In the ensuing discussion I will highlight the key features of the above sciences to show how the problems posed above were tackled.
The Biographical (rijal) Literature
The first step in verifying a report is to know the reality of the person reporting a piece of news. That is why Allah (swt) says:
يَا أَيُّهَا الَّذِينَ آمَنُوا إِنْ جَاءَكُمْ فَاسِقٌ بِنَبَإٍ فَتَبَيَّنُوا أَنْ تُصِيبُوا قَوْمًا بِجَهَالَةٍ فَتُصْبِحُوا عَلَى مَا فَعَلْتُمْ نَادِمِينَ
‘O you who believe! If a Fasiq comes to you with a news, verify it, lest you harm people in ignorance, and afterwards you become regretful to what you have done.’ [49:6]
Here the ‘illah for verifying or scrutinizing a report is the potential harm that will be caused by accepting a false report. It is on the basis of this ayah that the Muhadditheen began to seek out information about narrators in order to verify their narration. But what about recording and publicizing the defects of such narrators, what is the Shar’I justification for doing this? Al-Bukhari reported on the authority of ‘Aisha that: ‘A man asked permission to enter upon Allah's Apostle. The Prophet said, "Admit him. What an evil brother of his people or a son of his people." But when the man entered, the Prophet spoke to him in a very polite manner. (And when that person left) I said, "O Allah's Apostle! You had said what you had said, yet you spoke to him in a very polite manner?" The Prophet said, "O 'Aisha! The worst people are those whom the people desert or leave in order to save themselves from their dirty language or from their transgression.’  This hadith teaches us that in warning the Muslims from a harm it is allowed to backbite because the man Rasulullah was warning about is one man named ‘Uyaynah b. Hisn who outwardly showed that he was a Muslim thought in reality he was not a Muslim. Rasulullah wanted to warn the people about this man so he said what an evil man he is. This is indicated by the Prophet’s answer to A’isha when she asked him why he used bad language, he replied that he one who used bad language is the worst of people yet he (saw) used bad language to describe this man. Therefore the reason must be that he wanted to warn the people and not to abuse the man and hence when he met him he was very polite to him. Imam al-Qurtubi commenting on this hadith said: ‘The Hadith contains the permission to backbite the one who publicly shows his Fisq or Fahsh and the like from unjust rulers or those who call to innovation though its allowed to do it in a polite manner as long as long as it does not lead to compromising the Deen of Allah Ta’aala.’  Thus, when we come to narrators of hadith it is clear that unscrupulous hadith narrators are not only harmful to Muslims but to Islam itlsef and therefore their faults must be recorded so no hadith will be accepted from them.
The endeavor to verify the reports gave rise to the science of Rijaal (ie the knowledge and collation of the biography of narrators) and the Science of Jarh (disparagement) and Ta’deel (attestation). Information regarding the probity and precision of narrators were recorded whether the information was disparaging or confirmed the reliability. The honest defamation or Ta’n was considered part of the Deen since it was necessary to protect the Deen. In collecting this material the Rijal critics spared no one to the extent that the son would criticize his father. It is reported that ‘Some people asked ‘Ali b. al-Madeeni, the great Rijal scholar, about his father. He said: Ask somebody else. They repeated the question. He fell silent and then lifted his head and said: This (is part) of the Deen. He (my father) is weak (da’eef).’ It is for this reason that people like the great Tabi’I ‘Ata b. as-Saa`ib and well known Seerah writer Ibn Ishaq were not spared from criticism. Yayha b. Ma’een said: ‘We disparaged people who had already been admitted to Jannah more than a hundred years ago.’ Their prime motivation for doing this was fear of Allah and not the fear of the people. It is reported that Yahya b. Sa’eed al-Qattan was asked: Do you not fear that those people whose hadith you have rejected will dispute against you before Allah? He said: no, that these people should dispute with me is better than the Messenger of Allah (saw) disputing with me by saying: Why did you narrate a hadith which you thought was a lie?’
The Stringent Isnad Criteria
Five strict conditions were set to rigorously assess the authenticity of a hadith. The early pioneer in this field, as in so many other fields of Islamic learning, was the great Imam Shafi’I who spelt out a methodology to verify authenticity. Before Shafi’I people were taking munqati and mawquf hadiths until he came along and established the indispensability and supremacy of the muttasil (continuously liked) narration over all other forms of transmission. They were rejecting certain traditions because they seemed to contradict with other narrations. It was Shafi who devised a system of jam’ and tarjeeh to reconcile and outweigh the narrations. The two jurisprudential approaches prevalent in his time was the Ahlul hadith and Ahl ar-Ra’I who were either taking hadith which they should not take due to their weakness or rejecting sound hadith in favor of Qiyas. Shafi’I reconciled both approaches and set out a systematic methodology which was referred to by all the Mazaahib from that time onwards. So no one should underestimate the significance of following quote from ar-Risaalah which had such a profound influence on how the Ummah referred to the Sunnah in subsequent generations. In the chapter on ‘Proof of the Khabar al-Wahid’ Shafi states:
"Each reporter should be trustworthy in his religion; he should be known to be truthful in his narrating, to understand what he narrates, to know how a different expression can alter the meaning, and report the wording of the hadith verbatim, not only its meaning. This is because if he does not know how a different expression can change the whole meaning, he will not know if he has changed what is lawful into what is prohibited. Hence, if he reports the hadith according to its wording, no change of meaning is found at all. Moreover, he should be a good memoriser if he happens to report from his memory, or a good preserver of his book if he happens to report from it. He shouId agree with the narrations of thehuffaz, if he reports something which they also do. He should not be a mudallis, who narrates from someone he met something he did not hear, nor should he report from the Prophet contrary to what reliable sources have reported from him. The same qualification must be possessed by transmitters preceding him until the transmitter relates back to the Prophet or to him who carries it back to closest to him, for each of them vouches for the tradition as he received it and verifies it for him to whom he passes it. So none of them should lack the qualifications I have just described.’
In other words a Sahih hadith is a report ‘whose chain is continuous by the trustworthy and meticulous transmitters whose report contain no abnormality (shuzuz) or defects (‘illah).’  Thus, the conditions in this definition can be listed as the following:
1. Ittisal as-Sanad (continuity of the chain)
2. ‘adalatur ruwwaah (probity or trustworthiness of narrators)
3. Dab tar-Ruwaah (The precision and accuracy of narrators)
4. The absence of shuzooz and al-‘illah ie the absence of conflict with stronger narrations and hidden defects (‘ilal).
The continuity of the chain of transmission (Ittisal as-Sanad)
Isnad is the backbone of any report. Imam ash-Shafi’I used to say: ‘The one who looks for a hadith without Isnad is like the one who looks for firewood in the night.’ In other words he is groping in the dark and does not know what he is picking up. One of they key methods establishing continuity was the science of dates of birth and death of transmitters. Sufyan ath-Thawri said: ’when they (the fabricators) used lies we used dates’  By identifying when a narrators was born and when died it is possible to ascertain of there was a likelihood that he met the narrator from whom he claims he got the report. Look at the following example given by al-Khateeb in his al-Kifayah fee ‘ilmir riwaayah: Once a man named ‘Umar b. Musa came to Homs. The people gathered round him in the mosque and so he began speak: ‘We were informed by your pious Shaykh such and such hadith. When he kept mentioning him ‘Afeer b. Mi’daan asked him: Who is our pious Shaykh? Give us his name so we can identify him.
Umar b. Musa replied: he is Khalid b. Mi’daan.
‘Afeer asked him: which year did you meet him?
He said: I met him in the year 108 AH.
So he asked: where did you meet him?
He replied: I met him in the battle of Armenia.
So Afeer said: ‘Fear Allah O Shaykh and do not lie. Khalid b. Mi’dan died in the year 104 AH but you claim that you met him after his death by four years. Le me add he did not just fight in Armenia only but also fought the Byzantines.’
The weakest link in the chain is what makes or breaks the credibility of a report. So the Muhadditheen set out the classification of broken chains depending on where they occur and discussion of their value. For example a mu'allaq isnad is where one or more transmitters is missing at the beginning of the chain and mursal is when the Tabi’I omits the name of the sahabi. A mu’dal chain is where two or more transmitters are missing in one more place whilst the munqati’ is any break excluding mu’allaq, mursal and mu’dal. All of these chains are rejected except Mursal about which there is some difference of opinion. Some reject it, others like Abu Haneefah accept it because the omission of the Sahabi who is trustworthy is inconsequential whilst others accept it with certain conditions like Imam ash-Shafi’I. The usefulness of cataloging such chains is that it may be possible to fill the gap afterwards if other chains come to light which establish the continuity.
The Probity of Narrators (‘adaalatur ruwwaah)
After establishing continuity it is necessary to establish the trustworthiness of narrators. Since one can only go by the overt indications it is stipulated that for someone to be ‘adl he must not be known to be a liar or accused of lying or an open fasiq (ie someone who openly transgresses the ahkam) and he must be free from dishonorable behavior (khawaarim al-muroo’ah). Here we can see that it is not enough not to violate the Sharee’ah but the person must not violate the norms of society in order to be accepted by his peers. So, someone who constantly changes his opinion or (madhab) would be deemed as performing an action which may be permitted but would lose credibility i.e. such person would lose his ‘adaalah. Thus we can see the concept of ‘adaalah in narration of hadith is stricter than the concept of ‘adaalah when giving testimony before a Qadi. And finally, another disqualification of ‘adaalah is if the narrator is Majhool al-‘Ayn ie we know his name but do not known his reality.
The way we would know if someone is trustworthy if his probity is attested by other trustworthy people (mu’addileen or if they well known among scholars such as Sufyan b. ‘Uyaynah, Sufyan ath-Thawri or al-Awza’I.
The Precision (dabt) of Narrators (Dab tar-Ruwwaah)
Dabt is the precisian and accuracy of narrators in taking and conveying information. One of the qualities of a transmitter who is dabit is that he must be very alert and cautious lest he records a report from his master in which tadlis has occurred. Yahya b. Qattan heard Shu’ba saying : ‘I used to sit with Qatada (to learn hadiths from him). When he used to say ‘I heard such and such person say...’ I would write it down, but when he would say ‘ such and such person said (without specifying the sama’ from him)I would not write that report down’.  Above all he must verify and be meticulous in anything he transmits or receives.
Human beings naturally make mistakes but the one who is dabit should not make too many mistakes. Al-Ramhurmuzi reported form ‘Abd ar-Rahman b. al-Mahdi who said: ‘The Muhaddithoon are three types: The one who is of good memory and meticulous and there is no disagreement about him. The one makes mistakes but most of his haidth are sound and his hadith is not left. And the one who makes mistakes in the majority of his hadiths and this ones hadith is rejected (matrook).’  Thus the narrator must have a good retentive ability and not contradict the narrations of more trustworthy narrators.
Sometimes it can happen that a good narrator of hadith loses his retentive abilities later in life in which it case it is necessary to identify when a hadith was received from him. Ibn Lahee’ah started to muddle up his reports after his books got burned and so the muhaditheen stopped narrating from him father that point. Ahmed b. Hanbal said: ‘Anyone who had heard Ibn Lahee’ah long ago is valid (for report).’ The way in which dabt was ascertained is if his reports generally agree with other trustworthy narrators.
Absence of Shuzooz and ‘Illah
A hadith is considered Shaz when an acceptable transmitter transmits a matn or sanad which contradicts the matn or sanad of more trustworthy narrators. This is different to the munkar which is the narration of untrustworthy narrator which goes against the report of other trustworthy narrators. The benefit of this study is that one can detect mistakes and fabrications while at the same time assess the dabt and ‘adaalah of transmitters.
As for the study if ‘ilal or hidden defects this is one of the most delicate and difficult work of a Hadith critic. Whilst in Usul al-Fiqh it is enough to grasp the intellectual aspects and the key discussions but in the science if ‘Ilal one needs a breadth of knowledge which can encompass and recall a mass of reports and their asaneed in order to compare and detect that which is undetectable to the untrained eye . In this regard the Muhaddith is like a detective looking for clues which will allow him to trace a mistake to its source. Few have mastered this field due to breath of knowledge required to undertake such an investigation. al-Bukhari, Ali al-Madeeni and ad-Daarqutni are a few examples of those who became proficient in this branch of ‘Ilm al-Hadith. Ibn Hatim al-Razi sums it up nicely when he says: ‘The goodness of a Dinar is known when it is measured against another. Thus if it differs in redness and purity, it will be known known that it is fake. The kind of diamond if examined through measuring one another. If it differs in sparkle and firmness, it will be known to be glass. The authenticity of a hadith is known by its coming from reliable narrators and the statement itself must be worthy of being the statement of the Prophethood.’ 
The hidden defects can exist in the matn and sanad, and it is the task of the Isnad critic to detect the fault through a scrutiny of multiple narrations and also rectify the defect where possible. For example Yu’la b. ‘Ubayd narrated from ath-Thawri from ‘Amr b. Dinar that the Messenger (saw) said: ‘The seller and the buyer have the right to keep or return goods.’  Here Yu’la has made a mistake because it should be Abdullah b. Dinar and not ‘Amr b. Dinar who should be in the Isnad. How was it possible to catch this? This was because all the students of ath-Thawri reported the hadith from Abdullah b. Dinar and not ‘Amr b. Dinar and therefore Yu’la must have made the mistake.
Grading and classification of Ahadith
The hadith has been further graded  as Sahih, Hasan and Da’eef.
Once it has been established that a hahdith has a continuous isnad, made up of reporters of trustworthy preservers from similar authorities, and which is found to be clear from shuzuz and any hidden defects then the Hadiths is classed as Sahih. As for the Hasan Al-Khattabi (d. 388) states: ‘It is the one where its source is known and its reporters are prominent. It is the most regular hadith, and most scholars accept it, and it is used by the fuqaha generally’  Hasan however comes in two varieties:
i. one with an isnad containing a reporter who is mastur (i.e., no prominent person reported from him) but is not totally careless in his reporting, provided that a similar text is reported through another isnad as well;
ii. one with an isnad containing a reporter who is known to be truthful and reliable, but is a degree less in his preservation of hadith in comparison to the reporters of sahih ahadith.
In both categories however the hadith should be free of any conflict with more reliable narrations (shuzuz).
As for the Da’eef it is the narration which lacks the attributes of Sahih and Hasan. Whilst the last two are sound and relied upon as evidence Da’eef on the other hand cannot be adduced as proof.
After this the hadith were divided according to the manner in which it was transmitted to us. Although people disagreed about he details a basic distinction which everyone one accepts is that hadiths are either Ahad or Mutawatir.
Techniques in Averting Errors
A number of measure have been adopted to insure that errors are kept to a minimum. For example the use of textual comparisons. Cross-comparisons were made between the hadiths of different students of a given scholar or the statements of a scholar made at different times. Written versions were also compared with the oral record. Dabt, for example, was measured by using this procedure. In fact, this was the earliest method of checking the accuracy and truthfulness of traditionalists. There are reports which indicate that even Companions such as Abu Bakr, Umar b. al-Khattab and ‘A’isha cross examined people purporting to know traditions from the Prophet. This practice was continued by the Successors and developed to greater degrees of sophistication. The Successor, Ayyub al-Shakhtiani (d.131) used to say :’If you wish to know the mistakes of your teacher, then you ought to sit with others as well’.
This was the key technique in detecting interpolations (mudraj) in the text. For example, al-Khatib relates via Abu Qattan and Shababa --- Shu'ba --- Muhammad b. Ziyad --- Abu Huraira --- The Prophet, who said,
"Perform the ablution fully; woe to the heels from the Fire!"
Al-Khatib then remarks,
"The statement, 'Perform the ablution fully' is made by Abu Huraira, while the statement afterwards, 'Woe to the heels from the Fire!', is that of the Prophet. The distinction between the two is understood from the narration of al-Bukhari, who transmits the same hadith and quotes Abu Huraira as saying, "Complete the ablution, for Abul Qasim said, 'Woe to the heels from the Fire!'."
They used these techniques to detect alterations to the expression or meaning of a hadith. For example: The expression salla ila can mean to send blessings upon or to pray before something. Look at the misunderstanding of Abu Musa al-‘Anazi who said: we are a noble people for we are from ‘Anazah. The Messenger of Allah (saw) sent blessings meaning the hadith which says: anna an-nabi (saw) sallah ila ‘Anazah. He thought the prophet was seding blessings on his tribe when in fact what the statement meant is that the Prophet prayed before a ‘Anazah which is the name of spear placed in front of the Musalli when he prays.
Detection of forgery and deception
Techniques of detection came under two categories:
a) Techniques relating to the sanad.
b) Techniques relating to the matn or diraayah
In terms of the sanad there are times when a fabricator would confess, in such cases their names were recorded and narrations bearing that persons name were rejected. If a narrator did not meet the scholar from which he is narrating the tradition , or if he was born after the death of that scholars, or had not gone to the area or region from which claims he claims he heard the hadith, that would be an indication of fabrication. Also narrators lives were inspected if they had any vested interest in quoting a certain narration. Many hadiths were rejected using this technique. For example the hadith ‘The Hareesah (a certain dish) strengthens the back.’ It tuned out that its fabricator Muhammad b. Hajjaj an-Nakha’I used to sell Hareesah! 
As for the techniques relating to matn or what’s known as the study of Diraayah they include the following: The style and linguistic qualities of the texts were studied to see if they matched with the style of the Prophet which they had become accustomed to from well established authentic hadiths. Text containing corruptions and wild exaggerations in meaning were rejected or statements which were rationally unacceptable.  E.g. aubergines are the cure for all diseases. Texts which contradicted the Qur’an were also rejected. Also discarded were texts which contradicted well established facts of history during the time of the Prophet or when a narration agreed with sectarian views of extremely partisan narrators.
Perhaps one of the best examples of textual analysis is the one quoted by Ibn Qayyim in his Naqd al-Manqool. He quotes a report which says that an agreement was made with the people of khaybar exempted them from the payment of Jizyah.’ This report was declared a fabrication due to the following indications in the Matn:
i. Text mentiones Sa’d b. Mu’az but Sa’d had died before then in the battle of Khandaq.
ii. It mentions that Mu’awiyyah b. Abi Sufyan wrote the letter but Mu’awiyyah had not embraced Islam until the conquest of Makkah which is much later than this incident.
iii. The hadith mentioned Jizyah but that was not revealed until after Tabuk.
iv. It mentions that certain types of taxes were levied but these did not exist at the time.
v. The treaty us unspecified by time, how can this be when he did not grant them unspecified security?
vi. How could this happen without the knowledge of this who conveyed the Sunnah such as the Sahabah and Tabi’een but it so happens that the Jews know about it?
vii. The Jews of Khaybar fought Messenger and his companions, what did they deserve to be granted such an exemption from the obligation of Jizya, when other tribes just as bad were not exempted?
viii. Had the Prophet exempted them from the Jizya he would not have stipulated that they be expelled whenever he (saw) willed. This does not fit with the ruling that the Ahl al-Zimmah cannot be expelled as long as they abide by the rules of Islam.
ix. If the Prophet had exempted them when did none of the Sahabah exempt them? 
Science of Conflicting Hadith (Mukhtalaful Hadith):
It is inevitable that some reports will seem contradictory since one hadith may be general while the other is specific, or one is misquote while the other is accurate or if one has abrogated the other. Therefore, it was necessary to establish a methodology by which such seeming contradictions can be reconciled. It was for this reason that the science of Mukhtalaf al-Hadith was developed.
When presented with two sets of contradictory hadith one of three options are possible. Either one can resort to Jam’ or reconciliation of the hadith by considering whole host of issues such as textual indication (madlool al-Lafz) or if this is not possible then outweigh (tarjeeh) one report over the other if the chronology is not known and finally accept abrogation if the chronology known.
Imam al-Asnawi said: ‘When two evidences contradict then one is outweighed over the other if it is not possible to act upon both of them. If it is possible to act upon them even if it is from one aspect and not in another then we should not proceed to Tarjeeh (outweighing). This is because acting upon both evidences is better than neglecting one text completely since in origin a daleel should be acted upon and not neglected.’ 
Thus, the means of removing the contradiction are three:
a) Jam’ (reconciliation)
b) Tarjeeh (outweighing if the chronology is not known)
c) Naskh, abrogation if chronology is known.
d) If none of the above methods are possible then revert back to the original rule and assume the contradictory texts are non-existent.
The process of Jam’ is where you try to reconcile two contradictory texts due to certain linguistic and circumstantial considerations. For example the textual indications (madlul al-Lafz) can assist in the reconciliation between two texts. In one hadith it says: ‘Water is pure so nothing can make it impure.’  While another says: ‘If the water is enough to fill two pots (qullatayn), it carries no impurity.’  The first text is ‘Aam for all amounts of water but the mafhum of the second text indicates that water can become impure if its nature is changed. This is a specification (takhsees) of the first text by the mafhum of the second.
As for Tarjeeh this can happen in a number of ways. One way is if one of the conflicting hadith accords with another authentic hadith. For example one hadith says: ’There is no Nikah without a wali.’  This hadith stipulates the presence of a wali but it seems to contradicts with another hadith which indicates the wali is not stipulated. That hadith is as follows: ‘The matron has greater right than her guardians and the virgin her permission is sought. Her permission is her silence’  But the first hadith stipulating the presence of wali agrees with another sound narration which says: ‘Any woman who gets married without the permission of her guardian (Wali), her marriage will be void, her marriage will be void, her marriage will be void’  Therefore, the Tarjeeh will be that the hadith which says there is no nikah without wali is outweighed and accepted because it is supported by another authentic narration.
As for abrogation this happens when Jam’ is not possible but abrogation is possible because the chronology is known. For example one hadith says: ‘The one who cups blood and is cupped has broken his fast.’ But another ahdith says: ‘That the Prophet (saw) was cupped while he was fasting.’ If we scrutinize the circumstances of these hadiths we find that first hadith took place in year eighth of the Hijrah during Fath while the second hadith is in the Farwell speech (Hijjatul Widaa’) in the year 10 after Hijrah. Thus, ash-Shafi’I took the view that the second hadith has abrogated the first thereby allowing the cupping of blood while fasting in Ramadan.
The Muslims rose to the challenge when the source of their way of life was being threatened by destructive activities of hadith fabricators. They were able to amass a data base of thousands of narrators, set out rigorous criteria to asses authenticity, classify and adopt a grading system for chains narrators, devise techniques to detect and avert mistakes and fabrications and adopt a methodology to reconcile the differences within certain texts. The result was the effective preservation of the ideology and its legislative capacity.
If we compare the system of Isnad to the modern system of historical analysis we will find the former much more sophisticated and successful in establishing the veracity of historical incidents and events. What the Muslims called a Da’eef hadith is perhaps stronger in historicity, in some of its forms, than modern sources such history textbooks, numismatics or historical criticism of literary texts. This is because Da’eef does not mean fabrication but that it did not satisfy our stringent criteria. So when Nizam al-Islam mentions that riwaayah or narration is the strongest and most reliable source of history, not archeological findings, it assumes knowledge of the above discussion of the Isnad system.
Thus, the Muslims protected their ideology, insured the legislative capacity and preserved their Islamic civilization. Muslim historiography in this regard is a testament to how the Ummah can solve her problems, progress and revive if she adopts the Islamic ‘Aqeedah as the basis for her thoughts, society and state.
Kamal Abu Zahra
 The Islamic state p.199
 Sahih Zarkashi’s al-Ijaabah li-iraad maa istadrakathu ‘aisha ‘alas Sahabah p.76
 Bukhari, Kitab al-Adab, hadith: 80
 See Fathul Bari and section on Ibn Hajars discussion of Aisha’s hadith.
 Taqreeb see page 37
 See al-Kifayah fee ‘ilm ar-Riwaayah pp119
 See Abu Bakr Ahmed b. ‘Ali b. Thabit ( al-Khatib al-Baghdad ), Kitab al-Kifaya fi ‘ilm ar-Riwaya ( al-Maktaba al-’ilmiyya bi al-Madina al-Munawwara, n.d.) see p.164.
 al-Muhaddith al-Fasil p.406
 see Abn Abu Hatim al-Razi, al-Jarh wat-ta’deel
 an-Nukhba an-nabhaniyyahp. 123. the hadith is in bukhari in kitab al-buyu’.
 ‘ghareeb in matn for some is like shaz (contradiction of thiqaat) but for others its just irregular but not a cause for ta’n……but gharaabah in sanad it is saheeh but point is it is low in value, hence Imam Malik said: ‘the worst knowledge is the ghareeb and the best knowledge is the zaahir narrated by the people.’
 Ma’aalim as-sunan, vol 1, p.11.
 See as-Siba’I, as-Sunnah wa makaanatuhu fit tashree’ al-Islami
 Al-Khatib al-Baghdadi says: ‘All the statements come under three categories. Of them one is to be known to be erroneous. The cause of this knowledge is that ‘Aql refused to accept it.’ [Kifayah p. 17]
 Naqd al-Manqool, Ibn Qayyim al-Jawziyyah, p.90-93
 Nihayat as-suwal vol 3 p.214.’
 Abu dawud.
 Abu Dawud
 Sahih Muslim