Numbers 18:15-20

15The first offspring of every womb, both human and animal, that is offered to the Lord is yours. But you must redeem every firstborn son and every firstborn male of unclean animals.

16When they are a month old, you must redeem them at the redemption price set at five shekels of silver, according to the sanctuary shekel, which weighs twenty gerahs.

17“But you must not redeem the firstborn of a cow, a sheep or a goat; they are holy. Splash their blood against the altar and burn their fat as a food offering, an aroma pleasing to the Lord.

18Their meat is to be yours, just as the breast of the wave offering and the right thigh are yours.

19Whatever is set aside from the holy offerings the Israelites present to the Lord I give to you and your sons and daughters as your perpetual share. It is an everlasting covenant of salt before the Lord for both you and your offspring.”

20The Lord said to Aaron, “You will have no inheritance in their land, nor will you have any share among them; I am your share and your inheritance among the Israelites.