Numbers 18:2

And thy brethren also of the tribe of Levi, the tribe of thy father, bring thou with thee, causing them to come near to the Sanctuary with him. for the purpose of ministering, that they may be joined unto thee, and minister unto thee, in the position of assistants in the worship of Jehovah; but thou and thy sons with thee shall minister before the Tabernacle of "Witness, as being actually in charge of the sacrifices and of the various acts of atonement connected with the offerings.