Numbers 18:7-8

7But you and your sons will carry out your priestly responsibilities for everything concerning the altar and for what is inside the curtain, and you will do that work. I am giving you the work of the priesthood as a gift, but an unauthorized person who comes near the sanctuary will be put to death.”

8Then the Lord spoke to Aaron, “Look, I have put you in charge of the contributions brought to me. As for all the holy offerings of the Israelites, I have given them to you and your sons as a portion and a permanent statute.