Based on the request of one of our readers for an article explaining this issue, the following is an extract from the book 'The Ark of Salvation' by Abdul-Kareem Hassan and Murad el-Adnany:
Disagreement among the scholars of Islam has centred on whether action is part of Imaan or something based on Imaan. Some of the scholars of Islam have held the view that belief is simply an inward adherence (`aqd bi'l-qalb) and verbal confession (shahadah bi'l-lisan). Other scholars, such as Abu Talib al-Makki in Qut-al-Qulub , have maintained that action is a part of belief and Imaan is incomplete without works according to the pillars of Islam.
Imam al Ghazzali in "The Foundations of the Articles of Faith" says there is no disagreement at all that anyone who combines in himself all three, i.e., inward adherence, verbal confession and works according to the pillars of Islam, will have his final abode in Paradise. Disagreement has occurred as to whether inward adherence and verbal confession is sufficient to bring men forth from Hell and prevent them from remaining there forever, in accordance with the hadith: "Whoever hath in his heart the weight of an atom of belief will be brought forth from Hell-Fire."[al-Bukhari, al-Tirmidhi]
Those that say action is a part of Imaan contend that the person who does not perform the action, like prayer, is a disbeliever. For this reason the Khawarij sect considered a person who did not perform an obligatory duty (wajib) or who performed a forbidden action (haram) as a disbeliever. In arriving at this opinion they made ta`wil (allegorical type of interpretation) of the verse of Quran "He who kills a believer intentionally, his recompense is Hell, to abide therein forever" [al Nisa` 4:93] and the authentic tradition of the Prophet: "A fornicator is not a believer when he does it, a drinker is not a believer when he drinks." [Muslim]. These evidences appear to support the view that committing a sin makes one a disbeliever. This opinion has been rejected by the scholars of Ahlal Sunnah. The verse quoted was revealed, according to Imam al-Ghazzali, for the particular situation of a person killing a believer because of his belief. As for the tradition, Ibn al Qayim al-Jawziya quotes Imam Ahmad as saying the subject of the tradition is that the person in committing the sinful act is no longer a believer, but he is still a Muslim. It does not mean a disbelief that takes a person out of the community of muslims. It is not like believing in part of the revelation and disbelieving in another part of it; this is real disbelief, about which there is no doubt in anyone's mind.
The Mutazilah school of thought said that the person who commits a major sin (kaba'ir), but performs some works according to the pillars of Islam, departs from true belief but does not become an unbeliever. He becomes a fasiq (reprobate), neither a believer nor an unbeliever, and will reside in Hell forever. The Mutazilahs opinion has been rejected by the scholars of Ahlal Sunnah on the grounds that they failed to understand the real meaning of the verses of Allah, such as "Surely I am indeed forgiving to him who repents, believes and does righteous good deeds, and then remains constant in doing them." [Ta-Ha 20:82]; and "And for such as will rebel against Allah and His Messenger for him is the fire of Hell, he shall dwell therein forever." [al-Jinn 72:23] These verses, and others wherein Allah couples good works with belief, are general statements, which also include specification, as proven by the verse: "Verily! Allah forgives not setting up partners in worship with Him, but He forgives whom he pleases other sins than that." [an-Nisa 4:116]. Thus freedom to forgive men sins, other than shirk (setting up partners with Allah), must be left to Allah. This is proven by the tradition: "Whoever hath in his heart the weight of an atom of belief will be brought forth from Hell fire.", and the verse : "As to those who believe and do righteous deeds, verily! We shall not suffer to be lost the reward of anyone who do a righteous deed." [al-Kahf 18:30] In the context of this verse how would Allah suffer the reward, not only of good deeds, but the belief itself because of one sin?
The Murjiah considered the sinner to be full of Imaan, making ta`wil (allegorical type of interpretation) of such verses as: "And whoever believeth in his Lord, need not fear either loss or wrong." [al-Jinn 72:13]; and "And they who believed in Allah and His Messenger are the men of truth, and the witnesses in the presence of the Lord; they shall have their reward and their Light; but as for the disbelievers and those who give the lie to Our signs, these shall be the inmates of Hell." [al-Hadid 57:19] they said that no believer would enter Hell fire, although he might commit every possible sin. Their fundamental doctrine consisted of the suspension ( irja' ) of judgement against believers who committed sin. For the Murjiah the sinner was a sinner because of his major sin, and the believer a believer because of his Imaan . The opinion of the Murjiah has been completely rejected by the scholars of Ahlul Sunnah. The Prophet Muhammad (peace be upon him) said: "Whoever hath in his heart the weight of an atom of belief will be brought from Hell fire." How could anyone be brought forth from Hell fire if he had not first entered therein?
The People of Sunnah (Ahlul Sunnah):
The people of the sunnah and the majority of the muslims consider that action is a fruit of the belief and the person who commits a sin is not a disbeliever unless the sin is in the creed itself, i.e., it contradicts the faith such as the worship of idols, ridiculing the Quran, denying prayer or fasting, or permits adultery or usury etc. The person who does not pray is a sinner, the person who denies the duty of prayer is a disbeliever . In other words, there is a distinction between conviction and action. Imam al Nawawi says in his introduction to Sahih Muslim, "The school of thought of the true believers is that no one from the people of the Qibla becomes a disbeliever through a sin or innovation ( bida ) or through following a desire. Only if he denies what is known by Islam of necessity does he at that time become an apostate and disbeliever, unless that is he is new to Islam."
Sheikh Ali al-Tantawi in his book "The Faith" says: "Scholars of Ahlul Sunnah are unanimous in their opinion that a person who commits a forbidden act without denouncing its prohibition or a person who neglects to do a duty but does not deny that it is a duty and expresses no contempt for it will no doubt be punished in the other world. But he will not be accused of blasphemy nor will he be condemned to the eternal fire of hell."
The Fruit of Belief :
Those that say that action is neither a pillar of Imaan nor a part of it, but rather a fruit of Imaan, they also acknowledge that sometimes action is a part of Imaan; Imam Qurtubi in his explanation of : "Surely the (true) faith with Allah is Islam." [al Imran 3:19] quotes, for example, the Prophet having said, "Faith consists of seventy-odd aspects, the lowest of which is removing an obstacle (off the road), and the highest the profession that `There is no Allah but Allah.' and modesty is an aspect of faith."[Bukhari, Muslim] In this regard Qurtubi also quotes the hadith concerning the Abd al Qays delegation. This delegation came to the Prophet from the Island of Bahrain during the conquest of Makkah. They represented the tribe of Rabi'ah. The Prophet enjoined that they have faith in Allah alone. He then asked them, `Do you know what faith is?' They answered, `Allah and His Messenger knows best.' He said, `It is the witness that there is no Allah but Allah and that Muhammad is the Messenger of Allah, observing the regular worship, giving the obligatory alms, and observing the fast of Ramadan. It is also that you give in alms the fifth of the booty."
Imam al-Ghazzali says: "It is not unlikely that good works be considered a part of belief, because they perfect and complete it, just as it is said that the head and hands are part of man. it is evident that a person will cease to be human if his head no longer exists; but he will not cease to be a human being if one of his hands is lost through amputation. Similarly both the magnificent ( takbir ) and the praise (tasbih ) [at the beginning of prayer] are considered a part of prayer, although it is not annulled with their omission. Therefore acceptance with the mind stands in relation to belief as does the head in relation to the existence of man [in this life], since the one depends for its existence upon the other and ceases to exist when the other no longer is. The remaining good works are like the limbs of the body, some are more important than the others. The Messenger said, `A believer is no longer a believer when he commits fornication.' Furthermore the Companions held the same opinion as the Mutazilah concerning the fact that a person ceases to be a believer when he commits the sin of fornication. What this really means is that such a person is no longer a real believer possessing a complete and perfect belief, just as the deformed individual whose limbs have been amputated is described as being no longer a human being; in other words he lacks that perfection which is beyond actual humanity."
 A Muslim who holds the prayer to be obligatory but through lack of concern neglects to perform it until its proper time is over has not committed unbelief; the Hanafis, Malikis, and Shafiis all hold this to be the case. Imam Nawawi says: "This is what the vast majority of early and later scholars have held. [al-Majmu]. The Hanbali scholars have held two views: the first being that such a person becomes an unbeliever while the second view is that he does not become an unbeliever, and this is what Ibn Qudama, in al-Mughni, has declared to be the soundest opinion. The Prophet, peace and blessings be upon him and his family, said: "Allah has made five prayers obligatory: whoever performs their ablution well and prays them in their time, completing the bowing, the humility, and the awe that is due to them, has entered a solemn pact with Allah to forgive him. And whosoever does not, has no pact with Allah: should He want, He will forgive him, and should He want, He will torment him." [Abu Dawud, Malik]. It is necessarily established that unbelievers will be tormented and enter Hell, yet the hadith indicates that Allah may chose not to punish the person who does not pray, a clear indication that someone who neglects to pray is not a disbeliever. The Muslims from the earliest times have considered the person who misses the prayer to be entitled to inherit by way of estate division and be inherited from, and washed and prayed over on death; this would not be the case for an unbeliever. [Ahmad ibn Naqib al-Misri, The Reliance of the Traveller, pp.881-884].
 Tantawi, The Faith, p.69.
 al Ghazzali, Ihya Ulum al-Din, The Foundations of the Articles of Faith, Translated by Nabih Amin Faris, pp115-116.