Numbers 18:3, 7

And they shall perform duties for you and the duties of the whole tent, but they shall not come near the furnishings of the sanctuary and the altar, or both they and you will die.

But you and your sons with you shall attend to your priesthood for everything that concerns the altar and inside the veil, and you are to perform service. I am giving you the priesthood as a service that is a gift, and the unauthorized person who comes near shall be put to death.”