What is the expiation for swearing by divorce after I said, "My wife will not enter her house," and am I obligated to prevent my wife from visiting her sister after this oath of mine?

An oath by divorce is subject to the same ruling as a contingent divorce; it cannot be canceled or revoked according to the majority of scholars. Thus, divorce occurs upon the fulfillment of the condition sworn upon, even if the husband merely intended to threaten. Our fatwa follows the opinion of the majority. Therefore, if the wife entered her sister's house, the divorce would occur. If it was not preceded by two divorces, the husband can reconcile with his wife as long as she is within her iddah (waiting period). Ibn Taymiyyah held the view that divorce does not occur upon breaking such an oath if the husband merely intended to threaten. The husband should help his wife maintain her ties of kinship and should not repeatedly swear by divorce.