mention in passing
mention (something) in passing
To say something, casually or as an aside, during a conversation. It wasn't the main focus of our discussion—he only mentioned it in passing. Karen mentioned the party in passing the other day, but she didn't go into detail.
mention someone or something in passing
to mention someone or something casually; to mention someone or something while talking about someone or something else. He just happened to mention in passing that the mayor had resigned. John mentioned in passing that he was nearly eighty years old.