What is the ruling on saying, "I swear by Allah that if you step foot outside the house, you are divorced," and then retracting the oath on the same night? And what must the husband do?

If you swore to your wife that she would not leave the house, and you intended to prevent her only for that night, and she did not leave, then you have fulfilled your oath and are not considered to have broken it if she leaves afterwards. However, if you swore to prevent her from leaving without specifying a time, and she then leaves, a divorce occurs according to the majority of scholars, and retracting the oath is of no benefit. Since this issue involves detail and scholarly disagreement, it is best to present it to a trustworthy scholar.