It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Hearts are of four types: (1) A pure and clean heart, which is bright like a lamp; (2) A heart enclosed in a covering, from which the covering can never be removed; (3) An inverted heart; and (4) A double-faced heart. Their details are as follows: The pure heart refers to the heart of a believer, its lamp is its light; the heart enclosed in a covering belongs to a disbeliever; the inverted heart is that of a hypocrite who, after attaining the knowledge of truth, denies it; and the double-faced heart is the one in which there is both faith and hypocrisy. In it, the example of faith is like that of a green plant, which is nourished by pure water, and the example of hypocrisy is like that of a boil, which grows due to pus and blood. Whichever of the two increases more, that one prevails.