Numbers 3:39-41

Young's Literal Translation

³⁹ All those numbered of the Levites whom Moses numbered -- Aaron also -- by the command of Jehovah, by their families, every male from a son of a month and upward, [are] two and twenty thousand.

⁴⁰ And Jehovah saith unto Moses, `Number every first-born male of the sons of Israel from a son of a month and upward, and take up the number of their names;

⁴¹ and thou hast taken the Levites for Me (I [am] Jehovah), instead of every first-born among the sons of Israel, and the cattle of the Levites instead of every firstling among the cattle of the sons of Israel.'