Numbers 18:7-8

7But thou and thy sons with thee shall attend to your priesthood for all that concerneth the altar, and for that which is inside the veil; and ye shall perform the service: I give you your priesthood as a service of gift, and the stranger that cometh near shall be put to death.

8And Jehovah spoke to Aaron, And I, behold, I have given thee the charge of my heave-offerings, of all the hallowed things of the children of Israel; to thee have I given them, because of the anointing, and to thy sons by an everlasting statute.