What is the ruling on someone who, in a state of anger, said to his family: "I swear by God that if my relative marries with me, my wife will be forbidden to me in this world and the hereafter," knowing that his relative did marry with him, and he did not consummate the marriage with his wife until after the wedding ceremonies, and she is unaware, and he did not intend to divorce her, and they have a daughter? And can his oath be expiated, and what is the expiation for an oath and its measure?

Scholars have differed on the ruling concerning swearing by what is forbidden (al-haram). Some have held that it constitutes zihar (a pronouncement by a husband likening his wife to an unmarriageable female relative, which has legal implications), some that it constitutes talaq (divorce), and some that it constitutes an oath (yamin). The preponderant view is that a distinction is made based on whether the intention behind it was divorce, zihar, or an oath. Since you did not intend divorce or zihar by this prohibition, its ruling is that of an oath by Allah, and you are liable for an expiation for breaking an oath (kaffarat yamin): feeding ten poor persons, clothing them, or emancipating a slave. If you cannot find any of these, then fasting for three days.