Numbers 18:17-19

17But the firstborn of a cow, 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 burn their fat as an offering made by fire for a sweet aroma to the Lord.

18And their flesh shall be yours, just as the wave breast and the right thigh are yours.

19“All the heave offerings of the holy things, which the children of Israel offer to the Lord, I have given to you and your sons and daughters with you as an ordinance forever; it is a covenant of salt forever before the Lord with you and your descendants with you.”