Looking for a film example! Help!

Hey! I'm writing a philosophy paper, and am trying to make the point about being able to identify your future self in the instance of time travel. I know that I have seen this in a film at some point, but I can't for the life of me remember which one. Something along the lines of them asking "what's only something I would know?" in order to check it is really them. Any help is massively appreciated!