Numbers 18:1; Numbers 18:7

1 The LORD said to Aaron, “You, your sons and your family are to bear the responsibility for offenses connected with the sanctuary, and you and your sons alone are to bear the responsibility for offenses connected with the priesthood.

7 But only you and your sons may serve as priests in connection with everything at the altar and inside the curtain. I am giving you the service of the priesthood as a gift. Anyone else who comes near the sanctuary is to be put to death.”