Definition & Meaning of "says who"

What is the origin of the idiom "says who" and when to use it?

The idiom "says who" is an informal and often confrontational expression used to question or challenge the authority, credibility, or source of a statement or claim. It is typically used when someone wants to know the basis for another person's assertion or to seek confirmation of what has been said. The origin of this phrase is not precisely documented.