Numbers 18:15-17

LEB(i) 15 All the first offspring of a womb of any creature that they offer to Yahweh, whether human or animal, will be yours; you will surely redeem the firstborn of the human and the unclean firstborn of the animal. 16 As to their price of redemption, from a one-month-old* you will redeem them according to your proper value, five shekels of silver according to the shekel of the sanctuary, which is twenty gerah. 17 Only the firstborn of an ox or the firstborn of a sheep or the firstborn of a goat you will not redeem; they are holy. Their blood you will sprinkle over the altar, and their fat you will turn into smoke as an offering made by fire, a fragrance of appeasement for Yahweh.