Exodus 29:27-28

27You must keep separate this meat from the sheep's ribs, as well as the top part of its right leg. Those are the pieces that you lifted up to the Lord as an offering to him. Those pieces belong to Aaron and his sons.

28In the future, when the Israelites bring a peace offering to the Lord, these pieces will belong to Aaron and his descendants. This will always be the regular gift from the Israelites to the priests. That is the law that will continue for ever. It is the gift that the Israelites must bring to the Lord.