The Sunna Recorded in Hadith Is a Binding Source of Law

The Quran is, by universal Muslim agreement, the first source of Islamic law, but it does not by itself supply the detail a functioning legal and devotional system needs: the exact form of the five daily prayers, the precise rates owed in almsgiving, the particulars of marriage and inheritance are worked out from a second source, the Sunna, the Prophet Muhammad's own recorded example. The Sunna reaches later generations through hadith, individual reports of what the Prophet said, did or approved of, each one carried by a chain of named transmitters, an isnad, stretching back to someone who witnessed it directly. Because the reliability of a hadith rests entirely on the reliability of that chain, Islamic scholarship developed an entire discipline, the science of hadith criticism, to grade each report by how trustworthy and how unbroken its chain of transmitters is, sorting reports into ranks from sound, sahih, down through acceptable, hasan, to weak, da'if, and lower still. Which specific collections of hadith a tradition treats as most authoritative differs across the branches of Islam, but the underlying claim, that the Sunna stands as a binding source of law second only to the Quran itself, is shared ground across nearly the entire faith.

Agreement that the Sunna binds does not extend to agreement on which collected hadith texts carry that authority most reliably, and the resulting canons differ by branch of Islam. Sunni scholarship settled, over the centuries following the Prophet's death, on six major collections as its most authoritative core, among them Sahih al Bukhari and Sahih Muslim, both compiled in the ninth century and both still regarded as the two most rigorously verified Sunni hadith collections in existence. Twelver Shia scholarship developed its own parallel canon instead, the Four Books, compiled independently of the Sunni six and giving particular weight to hadith transmitted through the Prophet's family and his close companion Ali, a preference that follows directly from Shia doctrine about who held rightful religious authority after Muhammad. A small minority current within modern Islam, sometimes called Quranist, goes further still and rejects binding authority for hadith altogether, holding that only the Quran itself carries that standing and that centuries of hadith transmission introduced too much room for error and fabrication to be trusted as law. That position remains a minority one against the great weight of Sunni and Shia scholarship alike, both of which, despite disagreeing sharply on which hadith to trust, agree that some body of transmitted Sunna is indispensable to Islamic law.