In Islam, a Fazail is a book that contains a collection of hadith. These are the words or deeds of the Prophet and his companions that Islam considers important. In general, a Fazail can be considered to be similar to a religious book in other religions.

In the hadith, the Prophet is reported to have said: "There is a day when the Earth will be filled with the knowledge of the deeds of the righteous."

The word Fazail is derived from the Arabic word Fazāil which means "Those who are informed of his [the Prophet's] deeds" and "those who learn about his [Prophetic] knowledge".