As for those in whose hearts is disease, they are mentioned repeatedly in this surah. They are mentioned here, and in His words:

“If the hypocrites, those in whose hearts is disease, and those who spread rumours in Medina do not desist…”

And in His words:

“Lest one in whose heart is disease should be moved to desire.”

Allah mentions disease of the heart in several places. He Most High says:

“When the hypocrites and those in whose hearts is disease said, ‘Their religion has deluded these people.’”

Disease in the heart is like disease in the body. Just as bodily disease is a departure from health and balance without death, so too the heart may suffer a disease that takes it away from health and balance without causing it to die, whether it impairs the heart’s perception and understanding or its actions and impulses. As they have explained, this stems from weakness of faith: either weakness in the heart’s knowledge and conviction, or weakness in its actions and impulses. This includes those whose belief is weak and those overcome by cowardice and fear. The heart’s ailments—unlawful desire, envy, cowardice, miserliness, and the like—are all diseases, as are the ignorance, doubts, and misconceptions within it.

Accordingly, the statement:

“Lest one in whose heart is disease should be moved to desire”

refers to the desire for sexual immorality and the lust for illicit intercourse, as they have explained it. Another example is the saying of the Prophet, may Allah bless him and grant him peace: