Is expiation obligatory upon one who swore by Allah to recover his money, but it was not returned to him?

One should not engage in such transactions until their permissibility and lawfulness are ascertained. As for the necessity of expiation (kaffarah) if what one swore an oath about does not materialize, there is a difference of opinion on this matter. The fatwa issued is that it is not obligatory. However, if expiation is offered as a precaution when there is despair of the money being recovered, that is good.