What is the ruling of Islamic law concerning a man who swore an oath of triple divorce upon his wife—being coerced by her insistence—that he would not engage in an illicit relationship, and then he engaged in such a relationship?

The husband has fallen into Sharia prohibitions that necessitate repentance. Among them: uttering three divorces with a single pronouncement. This contradicts the Sunnah of Prophet Muhammad, according to the consensus of the Four Imams, and some consider it a single divorce. The evidence for its prohibition is the Almighty's saying: "Divorce is twice," and "O Prophet, when you [men] divorce women, divorce them for [the commencement of] their waiting period." Another prohibition is the husband's return to what was forbidden to him of unlawful sexual intercourse, knowing that he had made his wife's divorce conditional upon it. This is a grave sin that necessitates repentance, as per the Almighty's saying: "And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way." As for his oath under his wife's insistence, it is not considered true coercion. The questioner is advised to refer to the Sharia court in their country.