From Longman Dictionary of Contemporary Englishdon’t waste your breathdon’t waste your breath (also save your breath) spoken used to say that someone will not be able to persuade someone else, so there is no point in trying Save your breath. She’s already made up her mind. Will he listen to me or will I just be wasting my breath? → breath
Examples from the Corpus
don’t waste your breath• Save your breath. He won't listen. 