The following is a translation from the Usul Al-Fiqh masterpiece of the Arabic book “The Islamic Personality Volume 3” by Sheikh Taqiuddin an-Nabhani. Please refer to the original Arabic for accurate meanings.
The wājib and the fard have one meaning, without distinction; the two are synonymous. As for what some of the mujtahideen held that if the ruling is established by a definite evidence such as the Qur’an and the mutawātir hadith then it is fard, and if it is established by a preponderant [dhanni] evidence like the solitary report [khabr al-wāhid] or legal analogy [qiyās] then it is wājib, then this position is arbitrary and without evidence. There is nothing in the language or the revelation to establish it, nor is it correct for this to be a conventional position for those who hold it, because convention [istilāh] is the application of names upon referents [musammayāt], and this issue is not of this sort, rather this matter is of the definition of a specific referent and thus it must be in accordance with the reality. The reality of this referent is that which the legislator decisively requested, regardless of whether that request was established by a definite or indefinite evidence. The issue is related to the indication of the address, not to its establishment.
The obligation is of two types with respect to its fulfillment [ā’da’]: the expanded obligation [fard muwassa’] like the salāt and the confined obligation [fard mudayyaq] like the sawm. If the time granted for the performance of the obligation is greater than that required to perform it, like the duhr salāt for example, then it is an expanded obligation. All the parts of that time comprise the time for the performance of that obligation, whereby the obligation is fulfilled and its benefit acquired.
An evidence for the expanded obligation is that the command to pray Dhuhr – his (saw) saying in the hadith related by Abu Dāwūd that, “Jibrīl led me in prayer twice near the House. He led me in Dhuhr when the Sun moved from its zenith by the size of a shoe lace…” until he said, “and he led me in ‘Asr when the shadow of a thing was twice its size.” This includes all the parts of the mentioned time. The intent of this hadith is not the implementation of the first act of the salāt in the first time and the last at its last, nor is it the performance of the salāt in every part of the mentioned time such that no part of it is without salāt, nor is it the specification of a particular part of the time in which the obligation is fulfilled. This is because there is no indication in the expression for any of these meanings. Hence there remains no meaning except that each part of the time is acceptable for the performance of the obligation, and that the mukallaf has the choice of performing it in any of these parts.
Thus the obligation is upon the mukallaf in all the parts of the time, and his performance of it in any part thereof fulfills the obligation, and he gains the benefit of the obligation. However the mukallaf must intend to perform the obligation in the first part of its time. If he delays the prayer from its beginning but with the intention of praying it within its time and then dies before the time is over he does not meet Allah as a sinner. As for if he preponderantly thinks that he will die before the time is over, he is sinful in delaying the performance of the prayer from its beginning even if he does not die. This is because in the case of the expanded obligation the mukallaf must know that he is able to perform it within its allotted time. If he believes that this will not be possible then delaying it is not permissible.
Upon this understanding the Hajj is an expanded obligation upon the person having the means to perform it. He can perform it any time after attaining capability [istita’ah]. However if he preponderantly believes that he will lose this capability before he has performed the Hajj, then he must perform it immediately upon realising that he will lose the capability.
All of this is in the case that the time for the obligation is more than what is needed to perform it. As for if the time is not so, like with the sawn, then its immediate performance is obligatory, and delaying it is not permissible. The one who delays it is sinful, and he must make up for it.
As for the obligation with respect to its performance [qiyām], it is of two types: the individual obligation [fard ‘ayn] and the collective obligation [fard kifāyah], and there is no distinction between the two in terms of obligation. The obligation is the same in both, and both are equally the decisive request for the performance of an action. The difference between the two is that the individual obligation is sought from each individual as an individual, whereas the collective obligation is sought from all the Muslims as a collective. If the action is established, the obligation is performed, regardless of it is performed by everyone or only some. If it is not established it remains an obligation on everyone until it is established.
This is the obligation with respect to the subject (the doer). As for with respect to the object, the obligation is of two types: wājib mukhayyar [obligation with options] and wājib muhattam [obligation without options]. The mukhayyar obligation is the one in which the mukallaf is given the choice between performing one of a number of actions. For example Allah says,
«لَا يُؤَاخِذُكُمُ اللَّهُ بِاللَّغْوِ فِي أَيْمَانِكُمْ وَلَكِنْ يُؤَاخِذُكُمْ بِمَا عَقَّدْتُمُ الْأَيْمَانَ فَكَفَّارَتُهُ إِطْعَامُ عَشَرَةِ مَسَاكِينَ مِنْ أَوْسَطِ مَا تُطْعِمُونَ أَهْلِيكُمْ أَوْ كِسْوَتُهُمْ أَوْ تَحْرِيرُ رَقَبَةٍ فَمَنْ لَمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ ذَلِكَ كَفَّارَةُ أَيْمَانِكُمْ إِذَا حَلَفْتُمْ « “Allah does not take you to account for what is unintentional in your oaths, but He accounts you for your deliberate oaths; for its expiation, feed ten destitute persons, on a scale of the average of what you feed your families, or clothe them, or manumit a slave. But whosoever cannot afford such, he should fast for three days. That is the expiation for your oaths when you have sworn…” (al-Ma’idah: 89).
Here the mukallaf is given the choice of feeding ten poor people or clothing them or freeing a slave, so the obligation upon him is not specifically determined, it is specified by the action of the mukallaf. As for the muhattam obligation it is what is imposed upon the mukallaf to perform without giving him the option to choose between various acts, such as the salāt, which is imposed upon him to perform without any option between it and something else.