The Quran is the most sacred text, as it is believed to be the literal word of God (Allah) as revealed to Muhammad. The Hadith is a secondary text that records the sayings of Muhammad and his followers. These two texts form the basis for all Islamic theology, practice, and Sharia (Islamic law).
Sunnah denotes the practice of the Islamic prophet Muhammad that he taught and practically instituted as a teacher of the sharī‘ah and the best exemplar.
Al-sīra al-Nabawiyya (Prophetic biography) is the traditional Muslim biographies of Muhammad from which, in addition to the Quran and trustable Hadiths, most historical information about his life and the early period of Islam is derived.