Should a clergyman attribute the (non-Biblical) source of words that he uses in a sermon?

I recently went to a memorial service for a friend who got killed.

In the course of the service the minister said a prayer, that contained the words “Let Creation reveal it’s secrets, by and by”.

I was really impressed with the phrase and could not get it out of my head.

Last night, I repeated it to the dad of a friend of mine, saying that I was really taken by the minister’s poetic skill.

He said, “Shit, that’s a line from a song”. He even knew the song.

I searched it, and sure enough, it is.

Not that I would ever make an issue of it other than ask the question. But shouldn’t a preacher give recognition to the author of a phrase that they use in sermon? Did he commit plagiarism?