be none of (one's) business
To not be something that one needs to know or worry about; to be something private. It's really none of his business what I do with the money I earn.
be none of somebody’s ˈbusiness
, be no business of somebody’s
(informal) a person has no right to know something: ‘How much do you earn?’ ‘That’s none of your business.’It’s no business of yours who I go out with.