Is an expiatory offering (kaffara) for an oath obligatory upon someone who swore by saying, "By God, you will expel us," intending to silence those with him, while not believing that the expulsion would actually occur? And is this oath considered a "vain oath" (laghw al-yamin)?

We warn the questioner against obsessive thoughts (waswas) and indulging in them, as they lead to great evil. If his oath was uttered unintentionally, it is an idle oath (laghw yamin) for which there is no expiation. Similarly, if he doubts whether it was an idle oath or a binding oath, the default is that his conscience is clear.