The burden placed upon man by the Islamic revelation, namely, henceforth to translate the revelation into laws or precepts for action, was a heavy one indeed. At least in the stream of Semitic religious consciousness, it was the first time that law was desacralized – and by religion itself; it was divested of its holiness as direct revelation. Henceforth, law was declared to be a human responsibility in the exercise of which humans were fallible. When done right, law is man's greatest accomplishment; when done wrong, his greatest downfall. At any rate, lawmaking was to be a human activity, capable, like every other human activity, of being right or wrong. When wrong, it is equally man's responsibility to discover the locus of error, to amend that law, and bring it into accord with the divinely given principles of which the law is the translation. Certainly it is an act of mercy that God chose to aid man in fulfillment of this obligation when He provided him with an example and clarification, a commentary of the general principles of the revelation. For that is precisely what the sunnah is.
Technically, the sunnah is a collection of the Prophet's sayings and deeds. It includes his opinions about matters good or evil, desirable or otherwise, as well as the practices of which he approved as becoming for Muslims to follow. The sunnah quotes the words and phrases attributed directly to the Prophet or to his companions who witnessed his attitudes and deeds and reported them. Every unit of the sunnah conveying a report about the Prophet is called a hadith. The sunnah occupies a place second to the Qur'an. Its function is to clarify the Qur'an's pronouncements, to exemplify and illustrate its purposes. Where the Qur'anic statement is general, the sunnah particularizes it to make it applicable; and where particular, the sunnah generalizes it in order to make possible its extrapolation to other particulars. The sunnah was first memorized by the companions of the Prophet as many of them found the time to record the Prophet's sayings in writing. Afraid that the new Muslims might confuse the word of God with the word of Muhammad, the Prophet had first prohibited the writing down of his own sayings. Later, when the possibility of confusing the two was removed by the majority's memorization of the Qur'an, the Prophet permitted his companions to write the sunnah. Among those companions who recorded some parts of the sunnah were Sa'd ibn 'Ubadah al Ansari (15/637), ‘Abdullah ibn Abu Awfa, Samrah ibn Jundub (60/680), Jabir ibn ‘Abdullah (78/698), Wahb ibn Munabbih (114/732) who inherited the collection of Abu Hurayrah (58/678); ‘Abdullah ibn ‘Amr whose writing recorded 1,000 or more hadith preserved in the Musnad of Ibn Hanbal; and 'Abdullah ibn 'Abbas (69/589) who left us a "camel load" of writing materials covered with hadith of the Prophet. Besides these, there was the covenant of Madinah, the constitution of the first Islamic state and the first constitution ever to be written. Dictated by the Prophet, its principles have remained operative throughout Islamic history. The main bulk of the sunnah, however, was not written until later. The first generation of Muslims memorized the sayings of the Prophet, taught them to one another, observed what they prescribed, and emulated what they described as the practice of Muhammad.
The value of the sunnah and its relevance to Islam was universally recognized by all Muslims. The need for it to help the Muslim fulfill the requirements of his faith in liturgical, legal, ethical, social, economic, political, and international affairs was felt by all. Hence, the sunnah came to be regarded, from the beginning, as a second authoritative source of Islam, whose dicta were binding on all Muslims. The Qur'an commanded obedience to the Prophet and equated that obedience with obedience to God. It ordered the Muslims to refer their disputes to him and to abide by his judgment. The Prophet's companions, for their part, obeyed that command and voluntarily fulfilled everything the Prophet had asked of them. It was their unanimous consensus that the sunnah of the Prophet is normative, that its precepts are binding on all Muslims. Indeed, the Muslims had no other source to provide them with the specific rituals of worship and institutions of their faith, and to legislate for them in matters on which the Qur'an is silent, save the sunnah. Naturally, there can be no contradiction between the Qur'an and the sunnah. Everyone of the latter's provisions must be either confirmed or implied by the Qur'an, whether explicitly, by a direct passage of the text, or implicitly, by a Qur'anic principle or desideratum whose realization necessitates the provision commanded by the sunnah.
However, not all that the Prophet said or did, approved or disapproved of, is normative and hence obligatory for Muslims to follow. The Prophet was not superhuman or divine but a human, all too human, being. The Qur'an repeated this fact many times, and the Prophet himself never tired of reaffirming this basic truth. As a human being he did, said, approved and disapproved of many things outside of his function as executor of Qur'anic commands, as exemplar of the ethic of Islam, or as embodiment of the Islamic life-style. In this regard, Muslims distinguish between those items that issue from his prophethood and mission, and those that issue from his humanity. The former are accepted as normative without hesitation. The latter, in absence of evidence to the contrary, are treated as peculiar to him as a shepherd, tradesman, farmer, husband, general, statesman, paramedic, engineer, and so on. Muslims regard the former as normative and the latter, otherwise; and in doing so, they are backed by the Prophet himself, who acknowledged and accepted on numerous occasions the contrary counsel or action of his companions. The sunnah, as a technical term or source of Islamic law and ethics, includes only those items that are proven to have been meant by the Prophet to be followed and obeyed in loyalty to his divine message.
The foregoing differentiation in normativeness divided the sunnah into two great divisions; one containing all those items that give rise to law and obligation (sunnah hukmiyyah), and one containing all those that do not (sunnah ghayr hukmiyyah). Within the former, various degrees of normativeness were discerned following two criteria: first, the degree of certainty of provenance (wurud) or the quality of our knowledge that those items issued from the Prophet and did so for the purpose of clarification or exemplification of the divine message; and second, the degree of certainty with which the specific connotation (dalalah), the exact identity, meaning, or form of that which is commanded, is known. This differentiation divided the sunnah hukmiyyah into qat’iyyah (absolutely certain) and zanniyyah (probable), and these divisions applied to both provenance and connotation. Obviously, legal obligation attached only to those items fulfilling the criteria of certainty in both respects.
During the lifetime of the Prophet, the sunnah was for the most part something witnessed in public. As it issued from the Prophet, people heard, saw, and understood. When they were not present and sought reassurance, they could and did refer to the Prophet and asked him directly, face to face, to satisfy their quest. After his death, the companions asked one another. When all those who attended or witnessed the event agreed, their unanimity was tantamount to certainty. For it is not possible that the Prophet's companions, with all their loyalty and sincerity, their personal differences and distinctions, could come up with the same report unless the event was real and its meaning was absolutely clear. Items of the sunnah that fit this description were called sunnah mutawatirah. The sunnah mashbuhah refers to those items that were reported by some companions - not all whose consensus could not have involved mistake, error, or misrepresentation; while sunnah ahad includes items reported by one companion known for his good memory, fidelity, and moral integrity.
Across these divisions lies the distinction between fi`liyyah (action) and qawliyyah (verbal). The former refers to deeds of the Prophet, done once, occasionally, or repeatedly under the witness of the public. To this group belong the rituals and institutions of Islam which continue to be practiced throughout the Muslim world with astounding identity despite the centuries that separate their practice from the Prophet and the total discontinuity of geography, ethnicity, language, and culture among the world's followers of the Prophet. The latter comprises the Prophet's sayings heard by others and necessarily involving a lesser degree of certainty than something witnessed, unless - again like the rituals and institutions - they were repeated on a daily, weekly or yearly basis.
The sunnah thus was heard, witnessed, memorized, recorded, and transmitted to posterity. Since the third century A.H., it has been known through six canonical collections called the sihah (sing. sahih). By order of the rigor with which they carried out their sifting and classification, the collectors of the sihah were al Bukhari (256/870), Muslim (251/865), Abu Da'ud (275/888), Ibn Majah (273/886), al Nasa'i (303/915), and al Tirmidhi (279/892). Among these, the first two stand apart, acknowledged by all Muslims as more critical and authoritative than the rest. Those items commonly found in both their texts are most authoritative of all.