none of one's business
Not one's concern, as in How much I earn is none of your business. This expression employs business in the sense of "one's affairs," a usage dating from about 1600. (Also see mind one's own business.) A slangy, jocular variant from about 1930 is none of one's beeswax. The related verb phrase have no business is used to indicate that one should not meddle or interfere, as in He has no business discussing the will with outsiders.