mention in passing

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.
See also: mention, passing

mention (somebody/something) in passing

to refer to someone or something briefly while talking about something else During the interview, she mentioned in passing that her father had also been involved in publishing.
See also: mention, passing
References in classic literature ?
It is necessary to mention in passing the celebrated Ch`u Yuan(fourth cent.