(Arabic: “habitual practice”), the body of traditional social and legal custom and practice of the Muslim community. In pre-Islāmic Arabia, sunna referred to precedents established by tribal ancestors, accepted as normative, and practiced by the entire community. The early Muslims did not immediately concur on what constituted their sunna. Some looked to the people of Medina for an example, others followed the behaviour of the Companions of Muḥammad, whereas the provincial legal schools, current in Iraq, Syria, and the Hejaz (in Arabia) in the 8th century AD, attempted to equate sunna with an ideal system—based partly on what was traditional in their respective areas and partly on precedents that they themselves had developed. These varying sources, which created differing community practices, were finally reconciled late in the 8th century by the legal scholar ash-Shāfiʿī (767–820), who accorded the sunna of the Prophet Muḥammad, as preserved in eyewitness records of his words, actions, and approbations, and known as the Ḥadīth, normative and legal status second only to that of the Qurʾān.

The authoritativeness of the sunna was further strengthened when Muslim scholars, in response to the wholesale fabrication of hadiths by supporters of various doctrinal, legal, and political positions, developed ʿilm al-ḥadīth, the science of attesting the authenticity of individual traditions. The sunna was then used in tafsīr, Qurʾānic exegesis, to supplement the meaning of the text, and in fiqh, Islāmic jurisprudence, as the basis of legal decisions not discussed in the Qurʾān. See also ilm al-ḥadīthʿ; tafsīr.