Numbers 18:17-19

17But the firstborn of a cow, or the firstborn of a sheep, or the firstborn of a goat, you shall not redeem; they are holy. You shall sprinkle their blood on the altar and shall burn their fat as a food offering, with a pleasing aroma to the Lord.

18But their flesh shall be yours, as the breast that is waved and as the right thigh are yours.

19All the holy contributions that the people of Israel present to the Lord I give to you, and to your sons and daughters with you, as a perpetual due. It is a covenant of salt forever before the Lord for you and for your offspring with you."