What is the ruling on someone who said, "This money is unlawful for me," but then recanted and took it?

Scholars differed concerning the prohibition of what is lawful (tahreem al-halal). Some are of the view that it is an idle utterance (laghw), except in the case of prohibiting one's wife. Others are of the view that it necessitates an expiation for an oath (kaffarat yameen), and this is the more preponderant opinion.