Numbers 18:17-18

17“However, you may not redeem the firstborn of cattle, sheep, or goats. They are holy and have been set apart for the Lord. Sprinkle their blood on the altar, and burn their fat as a special gift, a pleasing aroma to the Lord.

18The meat of these animals will be yours, just like the breast and right thigh that are presented by lifting them up as a special offering before the altar.