What is the expiation for one who swore an oath of divorce after a dispute with his wife's family, knowing that the official marriage contract has not yet been formalized?

The majority of scholars hold that whoever swears an oath by divorce and then breaks it, his wife is divorced, whether he intended divorce or merely a threat. Some scholars, like Ibn Taymiyyah, are of the opinion that one who swears by divorce for the purpose of a threat is obligated to offer an expiation for an oath (kaffarat yamin), and his divorce does not occur. The fatwa (religious edict) is based on the opinion of the majority. Therefore, if you enter your wife's family's house, the divorce occurs. You may take her back before the expiration of her waiting period (iddah), provided this was not the third divorce. Swearing by divorce is among the oaths of the wicked, and grave consequences may result from it.