A Hadīth (Arabic: حديث) (plural: hadith, hadiths, or ahādīth) is a saying or an act or tacit approval or disapproval ascribed either validly or invalidly to the Islamic prophet Muhammad.
Hadith are regarded by traditional Islamic schools of jurisprudence as important tools for understanding the Quran and in matters of jurisprudence. Hadith were evaluated and gathered into large collections during the 8th and 9th centuries. These works are referred to in matters of Islamic law and history to this day.
The largest denominations of Islam, Sunni, Shiʻa, and Ibadi, rely upon different sets of hadith collections.
Clerics and jurists of all denominations classify individual hadith as sahih (authentic), hasan (good) and da'if (weak). However, different traditions within each denomination, and different scholars within each tradition, may differ as to which hadith should be included in which category.
Hadith Qudsi (or Sacred Hadith) is a sub-category of hadith which are sayings of Muhammad. Muslims regard the Hadith Qudsi as the words of God (Arabic: Allah), repeated by Muhammad and recorded on the condition of an isnad. According to as-Sayyid ash-Sharif al-Jurjani, the Hadith Qudsi differ from the Quran in that the former are "expressed in Muhammad's words", whereas the latter are the "direct words of God".