Imān, or faith, in Islām is a belief that resides in the heart, is spoken with upon the tongue, and is reflected in one’s actions. It increases with obedience to Allāh, and decreases with disobedience. It includes belief in Allāh, His angels, His revealed books, His messengers, the Day of Judgment, and Qadr (Divine Decree), both the good and the bad of it. Imān increases with obedience to Allāh and decreases with disobedience.
The Prophet Muhammad (peace be upon him) described Imān in the following hadith:
“Imān is to believe in Allāh, His angels, His books, His messengers, the Last Day, and to believe in Qadr (Divine Decree), the good and the bad of it.”
— Sahih Muslim 8