Numbers 18:1, 7

Then the LORD said to Aaron: “You and your sons and your father’s house with you shall bear the iniquity related to the sanctuary, and you and your sons with you shall bear the iniquity associated with your priesthood.

Therefore 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.”