A hadith consists of two aspects: the text of the report (matn) containing the actual narrative; and the chain of narrators (isnad, or sanad), which documents the route by which the report has been transmitted.^[3] The "sanad" is so named due to the reliance of the hadith specialists upon it in determining the authenticity or weakness of a hadith.^{[clarification needed][5]} The sanad consists of a ‘chain’ of the narrators each mentioning the one from whom they heard the hadith until mentioning the originator of the matn along with the matn itself. The first people who received hadith were the companions; so they preserved and understood it, knowing both its generality and particulars, and then conveyed it to those after them as they were commanded. Then the generation following them, the Followers received it thus conveying it to those after them and so on. So the companion would say, “I heard the Prophet say such and such.” The Follower would then say, “I heard a companion say, ‘I heard the Prophet.’” The one after him (after the Follower) would then say, “I heard someone say, ‘I heard a Companion say, ‘I heard the Prophet …’’” and so on.^[6]

Traditions of the life of Muhammad and the early history of Islam were passed down orally for more than a hundred years after Muhammad's death in AD 632.

Muslim historians say that Caliph Uthman (the third khalifa, or successor of Muhammad, who had formerly been Muhammad's secretary), was the first to urge Muslims to write the Qur'an in a fixed form, and to record the hadith. Uthman's labours were cut short by his assassination, at the hands of aggrieved soldiers, in 656.

The Muslim community (ummah) then fell into a prolonged civil war, which Muslim historians call the Fitna. After the fourth caliph Ali ibn Abi Talib was assassinated in 661, the Umayyad dynasty seized control of the Islamic empire. Ummayad rule was interrupted by a second civil war (the Second Fitna), re-established, and ended in 758 when the Abbasid dynasty seized the caliphate, and held it, at least in name, until 1258.

Muslim historians say that hadith collection and evaluation continued during the first Fitna and the Umayyad period. However, much of this activity was presumably oral transmission from early Muslims to later collectors, or from teachers to students. If any of these early scholars committed any of these collections to writing, they have not survived. The histories and hadith collections we have today were written down at the start of the Abbasid period, more than a hundred years after Muhammad's death.

Scholars of the Abbasid period were faced with a huge corpus of miscellaneous traditions, some of them flatly contradicting each other. Many of these traditions supported differing views on a variety of controversial matters. Scholars had to decide which hadith were to be trusted as authentic and which had been invented for political or theological purposes. To do this, they used a number of techniques which Muslims now call the science of hadith.

At the beginning of the 7th century, those receiving the hadith started to question the sources of the saying. The hadith were eventually recorded in written form, had their Isnad evaluated, and were gathered into large collections during the 8th century.

Hadith are generally categorized as sahīh (sound, authentic), da‘īf (weak), or mawdū‘ (fabricated). Other classifications used also include: hasan (good), which refers to an otherwise sahīh report suffering from minor deficiency, or a weak report strengthened due to numerous other corroborating reports; and munkar (ignored) which is a report that is rejected due to the presence of a solitary and generally unreliable transmitter.^[8] Both sahīh and hasan reports are considered acceptable for usage in Islamic legal discourse. Classifications of hadith may also be based upon the scale of transmission. Reports that pass through many reliable transmitters at each point in the isnad up until their collection and transcription are known as mutawātir. These reports are considered the most authoritative as they pass through so many different routes that collusion between all of the transmitters becomes an impossibility. Reports not meeting this standard are known as ahad, and are of several different types.^[3]