What is the ruling on swearing to one's wife that she will not sleep in her family's house, with the intention of preventing her, considering that the oath was made with the intention of divorce only to scare her?

The majority of scholars hold the view that a divorce pronounced as a clear, suspended (contingent) statement takes effect upon the occurrence of the condition it was made contingent upon, whether the one swearing intended divorce or a threat. This is the preponderant view.

Accordingly, if you swore a clear oath of divorce that your wife would not sleep in her parents' house, and she did sleep there as intended, then divorce has occurred according to the majority of scholars.

In this case, you may revoke the divorce before the completion of her iddah (waiting period) if this divorce does not complete three divorces.

Sheikh al-Islam Ibn Taymiyyah stated that an expiation for an oath (kaffarat yamin) is required if the intention of the one swearing was to prevent (an action).

The oath is not broken if the wife sleeps in her parents' house after the specified period intended has expired, or if the reason for which you swore ceased to exist without any action from you. According to Ibn Taymiyyah, neither divorce nor expiation is required in this situation.