What is the ruling regarding a man who swore to his wife by divorce that she would not do a certain thing, and his intention was to divorce her if she did it, and the wife did the thing sworn upon, knowing that she was menstruating at the time of the oath and the husband was unaware of that?

If a man swears an oath of divorce that his wife will not do something, and she then does it, the divorce has occurred, especially if the husband intended divorce and not merely a threat. The fact that the wife is menstruating does not prevent its occurrence, for divorce during menstruation is effective according to the majority of scholars, despite its being an innovation (bid'ah). If this was the first or second divorce, the husband may take his wife back as long as she is within her waiting period (iddah).