Mentioning examples of idle oaths.

The Shaykh : Among the idle oaths is swearing about something one believes to be true, only for the matter to turn out otherwise. For example, a person says, "By Allah, I saw so-and-so yesterday," when in fact he saw a man who resembled him and assumed it was him. He then says, "By Allah, I saw so-and-so yesterday," but it later becomes clear that he did not see him. This is an idle oath for which no expiation is required of the person. Similarly, according to the stronger opinion, if a person says, "By Allah, so-and-so will arrive tomorrow," based on his belief that he will arrive, but he does not arrive, then no expiation is required of him. Why? Because he swore based on his belief; he believed that so-and-so would come tomorrow, so he said, "By Allah, he will arrive tomorrow," but he did not. Thus, no expiation is required of him, because he swore based on his belief, and one who swears based on his belief remains in that state of belief, so no expiation is required of him for that.