Numbers 18:6-8

And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are a gift, given unto Jehovah, to do the service of the tent of meeting. And thou and thy sons with thee shall keep your priesthood for everything of the altar, and for that within the veil; and ye shall serve: I give you the priesthood as a service of gift: and the stranger that cometh nigh shall be put to death. And Jehovah spake unto Aaron, And I, behold, I have given thee the charge of my heave-offerings, even all the hallowed things of the children of Israel; unto thee have I given them by reason of the anointing, and to thy sons, as a portion for ever.