Keep this to yourself
keep (something) to (oneself)
To not reveal or share some thought, idea, opinion, or piece of information with anyone else. I think it's best that we keep this to ourselves until we can determine what impact it will have. I don't want your advice, so if you have any suggestions, just keep them to yourself!
See also: keep
Keep this to yourself.
a phrase introducing something that is meant to be a secret. Andy: Keep this to yourself, but I'm going to Bora Bora on my vacation. Henry: Sounds great. Can I go too? John: Keep this to yourself. Mary and I are breaking up. Sue: I won't tell a soul.