Is expiation obligatory for a husband who said, "By the forbidden, this month shall not end with this woman still in my charge," meaning his second wife, and the month did end and she is still in his charge, then he divorced her twice and wants to take her back?

The preponderant view regarding swearing an oath by declaring one's wife unlawful is that if divorce is intended, it is a divorce; if ẓihār (a pre-Islamic form of divorce) is intended, it is ẓihār; and if an oath is intended, or if no specific intention is made, then it is an oath. The husband's breaking of his oath depends on his intention. If he intended the wife's separation before the end of the month, he breaks his oath if the month ends while she is still under his marital bond. If he intended only her divorce during the month, he fulfills his oath by divorcing her revocably. In the event of divorce or ẓihār, it applies to the wife he intended. If he did not intend a specific wife, then either it is confined to the one whom the context necessitates specifying, or he chooses by lot if he intended one unspecified wife, or it applies to both of them if there was no intention or specific context. It is preferable to present these matters to trustworthy scholars.