Hadith and Sunnah The earliest schools and scholars of Islamic law—starting around a century and a half after the death of Muhammad—did not all agree on the importance of Prophetic sunnah and its basis, the basis for which was the group of hadith ultimately attributed to Muhammad and his
followers. Opinion ranged from prophetic hadith being one source of law among others (such as caliphal tradition or reports going back to Muhammad's followers), as was held by the
ahl al-raʿy to outright rejection of hadith on the basis of their potentially tenuous historicity, as was held by the
ahl al-kalām (referred to by some as "speculative theologians").
Hadith canonization A sizable shift in practice in favor of the tradition of prophetic hadith and its basis for Islamic law (
fiqh) came with
al-Shāfiʿī (767–820 CE), founder of the
Shafi'i school of law. According to this school of thought, prophetic hadith override all other hadith. It is unlikely that consensus yet existed for this view at this time as Shafi'i would come to spend great effort on establishing and promulgating his views over other ones. For those who criticized the reliability of hadith on the basis of their long phase of oral transmission, al-Shafi'i responded by arguing that God's wish for people to follow Muhammad's example would result in God ensuring the preservation of the tradition. Sunnah became a source of divine revelation (
wahy) and the basis of classical Islamic law (
Sharia), especially in consideration of the brevity dedicated to the subject of law in the Quran (which, for example, does not comment in detail on ritual like
Ghusl or
Wudu, or
salat, the correct forms of salutations, and the importance of benevolence to slaves.) Al Shafi'is advocacy played a decisive role in elevating the status of hadith although some skepticism along that of earlier lines would continue.
Hadith authentication and collection Once (authentic) hadith had attained their elevated status among the group inspired by al-Shafi'i who sought to establish Islamic practice on the basis of the
Sunnah (Muhammad's deeds and sayings), the focus shifted amongst advocates of this group (who were called the
ahl al-sunnah, or the "People of the Sunnah") to delineating between reliable or "sound" (
ṣaḥīḥ) with unreliable hadith. The field that arose to meet this need came to be known as the hadith sciences (
ʻilm al-ḥadīth), and this practice had entered into a mature stage by the 3rd century of Islam.{{#tag:ref|The last compiler of the six Sunni
Kutub al-Sittah to die, al-Nasa'i, passed on in 303 AH, 915 CE; some of the classical the Shia
The Four Books were compiled later; Al-Shafiʿi had died in the middle of the second century A challenge the hadith sciences had to confront was the massive scale of hadith forgery, with
Muhammad al-Bukhari claiming that only ~7,400 narrations of 600,000 he investigated met his criteria for inclusion. Even among those 7,400, a large fraction were variants of the same report, but with a different chain of transmitters (
isnad). The criteria for establishing the authenticity (
sihha) of hadith came down to corroboration of the same report but from different transmitters, assessing the reliability and character of the transmitters listed in the chain (although Muhammad's companions, the
sahaba, were excluded from this as their association with Muhammad immediately guaranteed their character and competence), and the lack of gaps in the chain. By implication, defects in hadith might assumed to be associated with the lack of character (
ʿadāla) or competence (
ḍābiṯ) of its transmitters. It was also thought that such faulty transmitters could be identified and that the isnad was a direct reflection of the history of transmission of a tradition. Evaluation rarely looked at the content (
matn) of a narration as opposed to its isnad. Ultimately, evaluations of hadith remained haphazard between authors until the practice of the hadith sciences was standardized by
Ibn al-Salah in the 13th century. It is through the lenses of this framework, supplemented by some additional work from
Al-Dhahabi in the 14th century and
Ibn Hajar al-Asqalani in the 15th century, that Muslim scholars since understood the discipline. The first collections to be accepted as authoritative among Sunnis by the tenth century CE were the
Sahihayn, referring to
Sahih al-Bukhari and
Sahih Muslim. Even as the set of canonical texts grew, the Sahihayn remained the core of the canon, with Sahih al-Bukhari typically being viewed as the most pre-eminent of the two. The tenth century CE also saw the inclusion of another two collections to form a Four-Book canon, including the
Sunan Abi Dawud and
Sunan al-Nasa'i. This grew into a Five-Book canon in the twelfth century, when
Sunan al-Tirmidhi was added. In the same century, the modern Six-Book canon, known as the
Kutub al-Sittah, emerged. Depending on the list, the sixth canonical book was the
Sunan ibn Majah, the Sunan of
Al-Daraqutni, or the
Muwatta of
Malik ibn Anas. == Reliability of hadith ==