Numbers 18:8-9

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. 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 or guilt offerings, that part belongs to you and your sons.