What is the expiation for swearing by divorce for one who swore to his wife by divorce that she would return alone, but she returned accompanied by her uncle?

If a husband swears to his wife that she must return home alone, and she returns accompanied by her paternal uncle, the majority of scholars hold that the divorce is effective. The husband may reconcile with his wife before her iddah (waiting period) ends, provided this divorce does not complete the three divorces. However, Ibn Taymiyyah and those who agreed with him believe that an expiation for a broken oath (kaffarat yamin) is required if the husband did not intend divorce but merely threat. Nevertheless, the preponderant view is that of the majority.