In Islam, sunnah, also spelled sunna, are the traditions and practices of the Islamic prophet Muhammad that constitute a model for Muslims to follow. The sunnah is what all the Muslims of Muhammad's time evidently saw and followed and passed on to the next generations. According to classical Islamic theories, the sunnah are documented by hadith, and alongside the Quran are the divine revelation (wahy) delivered through Muhammad that make up the primary sources of Islamic law and belief/theology. Differing from Sunni classical Islamic theories are those of Shia Muslims, who hold that Imams interpret the sunnah, and Sufi who hold that Muhammad transmitted the values of sunnah "through a series of Sufi teachers".

Islam is an Abrahamic monotheistic religion centered on the Quran and the teachings of Muhammad, the religion's founder. Adherents of Islam are called Muslims, who are estimated to number approximately 1.9 billion worldwide and are the world's second-largest religious population after Christians.