Numbers 18:7-9 New International Version - UK (NIVUK)
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.’
Offerings for priests and Levites
8 Then the Lord said to Aaron, ‘I myself have put you in charge of the offerings presented to me; all the holy offerings the Israelites give me I give to you and your sons as your portion, your perpetual share. 9 You are to have the part of the most holy offerings that is kept from the fire. From all the gifts they bring me as most holy offerings, whether grain or sin[a] or guilt offerings, that part belongs to you and your sons.