…LET SLEEPING DOGS LIE…
If someone is told to let sleeping dogs lie, it means that they shouldn’t disturb a situation as it would result in trouble or complications.
Refrain from disturbing people or from debating topics not currently causing one any trouble.
Example: It may be that he used to live with Miss Bloggs; but I don’t think you ought to refer to that topic in front of his wife – it’s better to let sleeping dogs of that sort lie.