Numbers 18:15-17

15The firstborn of every living thing, human or animal, presented to the Lord belongs to you. But you must certainly redeem a human firstborn, and redeem the firstborn of an unclean animal.

16You will pay the redemption price for a month-old male according to your assessment: five shekels of silver by the standard sanctuary shekel, which is twenty gerahs.

17“However, you must not redeem the firstborn of an ox, a sheep, or a goat; they are holy. You are to splatter their blood on the altar and burn their fat as a food offering for a pleasing aroma to the Lord.