Is it permissible to kill an insane person who utters blasphemy when angry?

It is never permissible to kill a madman, even if he utters blasphemy. A madman is not held accountable by Islamic law for what he says or does while insane. Jurists have unanimously agreed that a madman lacks intellect, discernment, and legal capacity, and the pen has been lifted from him. The execution of the apostasy punishment is not entrusted to individuals; rather, it is the prerogative of the legitimate ruler.