What is the ruling regarding a husband having sexual intercourse with his wife before completing the expiation for his statement to her: "You are forbidden to me until the Day of Judgment," and is he sinful for that, and what must he do?

The statements of scholars indicate that prohibiting one's wife is considered dhahār, and therefore, it is not permissible for the husband to have intercourse with his wife until after performing the expiation (kaffarah). Whoever intentionally has intercourse with her before the expiation has committed a sin and must repent. One expiation is sufficient for him. If the husband has intercourse with his wife after paying part of the expiation, he builds upon what he has already paid.