[The Degree of Insanity That Lifts the Ruling of Divorce]

Answer—and Allah is the One who grants success: Insanity has many forms. In some, the insanity pertains to his wife in particular; in others, it pertains to his brother or some relative or friend rather than others. If the insanity pertains to the wife and he pronounces divorce, his case is examined: if he reports about her that which reason does not admit, and accuses her of what the intellect does not accept—then such a person is insane for this purpose, and his divorce is not judged valid, even if his dealings with other people proceed according to the standards of reason. This type of illness is common in our time; physicians call it a “psychological illness.”
If it be said: Do all rulings fall from him?
We say: They fall from him with respect to that which his insanity pertains to, but not otherwise, until the insanity takes full possession of him. When it does, then all rulings fall from him. Illness progresses in a person little by little: it may begin regarding the wife, then—if it persists—it extends beyond her, then … and so on.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1