Abu Dawud al-Sijistani reports in al-Masa’il (p. 365, no. 1767), ‘Abd Allah b. Ahmad in al-Sunnah (1/317), al-Ajurri in al-Shari‘ah (2/608), Ibn Battah in al-Ibanah, first part (2/812, no. 1111), al-Lalakai in Sharh al-I‘tiqad (5/1031), and al-Khallal in al-Sunnah (3/608, no. 1082), through various chains from Surayj b. al-Nu‘man, from ‘Abd Allah b. Nafi‘, who said: “Malik used to say: ‘Iman (faith) consists of words and deeds; it increases and decreases.’” The isnad (chain of transmission) is sound. Al-Lalakai also relates in Sharh al-I‘tiqad (5/1031, no. 1743): Muhammad b. al-Hasan b. Muhammad al-Warraq told us, saying: Ahmad b. Khalaf narrated to us, saying: Abu Isma‘il—i.e. al-Tirmidhi—said: I heard Ishaq b. Muhammad say: “I was with Malik b. Anas when Hammad b. Abi Hanifah said to him, ‘Abu ‘Abd Allah, we have an opinion we wish to present to you; if you find it acceptable we will adopt it, and if not we will abandon it.’ Malik asked, ‘What is it?’ He replied, ‘Abu ‘Abd Allah, we do not declare anyone an unbeliever because of a sin; in our view all people are Muslims.’ Malik answered, ‘How excellent—that is unobjectionable.’ At that point Dawud b. Abi Zunbur, Ibrahim b. Habib and others rose and said, ‘Abu ‘Abd Allah, this man espouses irja’ (the Murji doctrine).’ Hammad said, ‘My religion is the religion of the angels brought near; the religion of Jibril and Mikail and the angels brought near.’ Malik responded, ‘No, by God! Iman increases and decreases: “that they may increase in faith along with their faith” (Q 48:4).’ He then cited the verse in which Abraham says, ‘Yes, but so that my heart may be reassured’ (Q 2:260), observing that this reassurance of the heart constitutes an increase in faith.” Abu’l-Walid Muhammad b. Rushd states in al-Muqaddimat (1/37): “It is reported from Malik—may God have mercy on him—that he affirmed the increase of faith but refrained from explicitly saying that it decreases, for God Most High mentions only its increase. It is further related that on his death-bed he said to Ibn Nafi‘, who had asked him about the question, ‘You have wearied me; I have reflected on this matter and concluded that whatever increases must also decrease—and that is the correct view. God, exalted be He, knows best.’” For additional documentation of Imam Malik b. Anas’s explicit statements that faith both increases and decreases, see: al-Sunnah by al-Khallal (no. 1014); al-Sunan by al-Bayhaqi (10/206); and Hilyat al-Awliya’ by Abu Nu‘aym (6/…).