Numbers 18:17-19

17“But you must never buy back a firstborn ox, sheep, or goat. They are holy. Throw the blood from these animals against the altar, and burn the fat as an offering by fire, a soothing aroma to the Lord.

18But the meat is yours, like the breast and the right thigh that are presented.

19I am giving you, your sons, and your daughters all the holy contributions the Israelites bring to the Lord. These contributions will always be yours. It is an everlasting promise of salt in the Lord’s presence for you and your descendants.”