Exodus 29:26-28

Then take the breast of the male sheep used to appoint Aaron as priest, and present it before the LORD as an offering. This part of the animal will be your share. Set aside the breast and the thigh of the sheep that were used to appoint Aaron and his sons as priests. These parts belong to them. They are to be the regular share which the Israelites will always give to Aaron and his sons. It is the gift the Israelites must give to the LORD from their fellowship offerings.