What is the expiation for someone who falsely swore by the triple divorce, not knowing that he had the keys with him?

The preponderant opinion is that a husband's divorce does not take effect if he swore believing himself to be truthful and did not intend to lie. Therefore, he is not required to offer expiation. This is the view held by Ibn Taymiyyah and Ibn Baz. In this case, the divorce is considered akin to an unintentional oath (yamin al-laghw) where the swearer did not intend falsehood. It remains important to note that the permissible oath is by Allah Almighty, whereas swearing by divorce is among the oaths of transgressors.