Does a person's saying to another, "He will make you his heir" – meaning "He will kill your master" – constitute an exit from the fold of Islam, given that the speaker does not intend to mock God? If so, what must he do to repent, and how does he inform his community of this?

This phrase was originally said to slaves and animals, and its intent was to invoke death upon the owner. It might be used figuratively for free people without intending to supplicate against God. The original usage presents no problem unless it is intended as an unjust supplication against a Muslim. It is permissible if it is a type of supplication not meant literally, like the Arab sayings: "May his mother lose him" and "May his hands be covered with dust," as the Prophet, peace be upon him, said similar things. As for the other usage, which caused the problem, it does not intend to supplicate against God, and thus the problem is resolved, even though it is better to avoid it. Allah Almighty forbade phrases that resemble those used by the Jews, such as "Ra'ina" (tend to us / cause us to stumble).