Is expiation obligatory upon one who said, "I am ready to swear upon the Mushaf" concerning something he thought was his, then it turned out to be otherwise, knowing that he did not actually swear?

If someone takes an oath believing what they swear upon to be true, then no expiation is due from them, provided their belief does not change. Most scholars are of the opinion that expiation is not obligatory even if what they swore upon turns out to be contrary to what they believed.