Numbers 3:40-42

American Standard Version

⁴⁰ And Jehovah said unto Moses, Number all the first-born males of the children of Israel from a month old and upward, and take the number of their names. ⁴¹ And thou shalt take the Levites for me (I am Jehovah) instead of all the first-born among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel. ⁴² And Moses numbered, as Jehovah commanded him, all the first-born among the children of Israel.