Numbers 18:7-8

7But only you and your sons shall attend to your priesthood for everything concerning the altar and what is inside the veil, and you are to perform that service. I am giving you the work of the priesthood as a gift, but any outsider who comes near the sanctuary must be put to death.”

8Then the LORD said to Aaron, “Behold, I have put you in charge of My offerings. As for all the sacred offerings of the Israelites, I have given them to you and your sons as a portion and a permanent statute.