“Sunna” is the Arabic term for the prophet Muhammad’s way of life and legal precedent. It comes from the pre-Islamic Arab notion of Sunna as the way of life of a tribe, which is reflected in the Qur’an’s use of the word to mean “the ways of God” (Qur’an 33:37, 62) or “ways of life” of earlier peoples (Qur’an 3:137). The Sunna is an authoritative source in Islamic law because the Qur’an is understood as ordering Muslims to “obey God and obey the Messenger” (Qur’an 8:1) and to “take what the Messenger has ordained for you and desist from what he has prohibited” (Qur’an 59:7).
In the framework of Islamic law, the Sunna explains duties left unclear in the Qur’an, such as how to pray; replaces Qur’anic rulings; and adds new details of law and belief as well. Although the Qur’an is held by Muslims to be the literal word of God and the ultimate fount of all Islamic teachings, from the earliest period of Islam Muslim scholars recognized that the Sunna’s role as the lens through which the Qur’an was understood made it in effect more authoritative than the Qur’an. In providing the details for the general principles laid out in the Qur’an, the Sunna effectively defined what those principles were. The Sunna is not simply a list of Muhammad’s legal pronouncements about what is required or prohibited for Muslims. It denotes his behavior in general, from the details of his dress to his interaction with his wives. As a result many details of the Sunna are not black and white requirements or prohibitions; they are either behavior that is recommended but not required or behavior that is licit but not recommended.
Although Sunni Islam (the original Arabic term is ahl al-sunna wa’l-jamaʿa, “the people of the Sunna and the collective”) takes its name from the term “Sunna,” Shiʿite Muslims are equally committed to the ideal of imitating the prophet’s precedent. Shiʿite Islam simply has its own vision of the Sunna, namely the teachings of the prophet as transmitted by the twelve imams and elaborated by Shiʿite scholars.