Hadith

Every hadith has two parts. The isnad is the chain of transmission, a list of names running back from the compiler to a Companion who heard or saw the thing reported. The matn is the text itself, usually a few lines. The classical science concentrates overwhelmingly on the chain, on the reasoning that a report can only be as good as the people who carried it.

That produced rijal, the biographical evaluation of narrators: vast dictionaries recording when each transmitter lived, whom he studied under, whom he taught, whether he was truthful, whether his memory decayed in old age, whether he was known to have met the person he claims to quote. From this comes the grading. A sahih report has a continuous chain of upright and precise narrators with no hidden defect; hasan is sound but with a weaker link; daif is weak, through a break in the chain or a discredited narrator; mawdu is judged fabricated outright. A separate axis counts transmission lines: mutawatir reports come through so many independent chains that collusion is held impossible, while the great majority are ahad, transmitted singly, and jurists disagree about how much doctrinal weight those can bear.

The grading is a working tool, not a historical verdict everyone shares, and it is applied with judgement. Weak hadith are not simply discarded, many scholars permit their use in exhortation while refusing them in law. Different scholars have graded the same report differently, and grading disputes are a live part of Islamic scholarship rather than a settled inheritance.

Sunni Islam recognises six collections, the Kutub al-Sittah, all compiled in the ninth and early tenth centuries. Two stand above the rest, known jointly as the Sahihayn: the Sahih of al-Bukhari, who died in 870 CE, and that of Muslim ibn al-Hajjaj, who died in 875. Both selected a few thousand reports from far larger bodies of material they had collected, and Sunni consensus treats their contents as authentic, though individual reports have been challenged. The remaining four are the Sunan of Abu Dawud, who died in 888, al-Tirmidhi, 892, Ibn Majah, 887, and al-Nasai, 915. These are broader, arranged by legal topic, and include material their compilers themselves marked as weak. Earlier than any of them stands the Muwatta of Malik ibn Anas, a legal work built on Medinan practice.

Twelver Shia Islam has its own canon, the Four Books: al-Kafi of al-Kulayni, who died in 941; Man la yahduruhu al-Faqih of Ibn Babawayh, called al-Saduq, who died in 991; and Tahdhib al-Ahkam and al-Istibsar, both by al-Tusi, who died in 1067.

The two corpora differ because the criteria differ. Sunni hadith science holds the Companions of the Prophet collectively upright, so a Companion in a chain is not himself subject to criticism. Shia scholarship does not extend that presumption, holds a narrow set of early transmitters authoritative, and accepts as sound only chains running through the Imams of the Prophet's family, whose own sayings count as authoritative alongside the Prophet's. The result is not two versions of one collection but two largely separate bodies of material, with limited overlap and different authorities inside them.

A small distinct category is hadith qudsi, sacred hadith, in which the words are attributed to God but transmitted through the Prophet in his own phrasing. Muslims do not treat these as Quran: they are not recited in prayer, not part of the codex, and not covered by the claim of inimitability, but they are held to carry divine content.

A minority position rejects the whole apparatus. Quranists, sometimes called Ahl al-Quran, argue that the Quran is complete and self-sufficient, that hadith were written down too late to be trusted, and that they have carried into Islam rulings scripture never gave. The position has recurred since the nineteenth century, is strongest in South Asia and among some diaspora Muslims, and is rejected by every major Sunni and Shia institution, which regard the sunna as inseparable from the Quran's own instruction.

Academic scholarship raised a separate challenge. Ignaz Goldziher, in the 1890s, argued that many hadith reflect the political and doctrinal battles of the Umayyad and Abbasid periods rather than the Prophet's lifetime. Joseph Schacht, in 1950, went further: he held that isnads grew backwards, chains being extended to earlier authorities as the demand for authority rose, and that a chain reaching the Prophet is often a sign of lateness rather than antiquity. G. H. A. Juynboll developed methods for dating traditions by the point at which their chains fan out. Later scholars, working by comparing text and chain together across independent versions, have argued that a substantial core does trace to the first century of Islam. Muslim hadith scholarship engages this work but does not accept its premises, since the traditional science grades transmitters where the academic method treats the chain itself as evidence in need of explanation.