Numbers 18:7-8

7But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”

8The Lord spoke to Aaron, “See, I have given you the responsibility for my raised offerings; I have given all the holy things of the Israelites to you as your priestly portion and to your sons as a perpetual ordinance.