Numbers 18:7-8

7Therefore you and your sons with you shall attend to your priesthood for everything at the altar and behind the veil; and you shall serve. I give your priesthood to you as a gift for service, but the outsider who comes near shall be put to death.”

8And the Lord spoke to Aaron: “Here, I Myself have also given you charge of My heave offerings, all the holy gifts of the children of Israel; I have given them as a portion to you and your sons, as an ordinance forever.