When an insane person attacks and his assault cannot be repelled except by killing him, he may be killed. Indeed, if an animal attacks and its assault cannot be repelled except by killing it, it may be killed. Even if it is owned, according to the majority of scholars—including Mālik, al-Shāfiʿī, Ahmad, and others—the person who kills it is not liable to compensate its owner.

Abū Hanīfa, however, holds that he must compensate the owner because he killed it for his own benefit, just as if he had killed it out of dire hunger.

The majority respond that, in the latter case, the animal is killed for a reason attributable to the person, not because of the animal’s aggression (1), whereas here it is killed because of its own aggression (2).

In general, killing one who is not legally accountable—such as a child, an insane person, or an animal—to ward off their aggression [is permissible on the basis of scriptural texts and consensus, (3) except in certain instances] (4), such as when they are killed during raids or night attacks, by catapult fire, or to repel their assaults.

The hadith, “The pen has been lifted from three,” indicates only exemption from sin; it does not [indicate] (5) that prescribed punishment is precluded (6) unless supplemented by another premise—namely: anyone from whom the pen has been lifted is not subject to prescribed punishment. This premise is not self-evident, for one from whom the pen has been lifted (7) may sometimes be punished and at other times not be punished, and distinguishing between the two requires subtle knowledge. If an insane man sought to force a woman to submit to him and could not be repelled except by killing him, she would be permitted to kill him. Indeed, she would be required to do so according to the Sunnah and the consensus of the scholars.