Numbers 18:15-17

New Revised Standard Version Catholic Edition

¹⁵ The first issue of the womb of all creatures, human and animal, which is offered to the Lord, shall be yours; but the firstborn of human beings you shall redeem, and the firstborn of unclean animals you shall redeem. ¹⁶ Their redemption price, reckoned from one month of age, you shall fix at five shekels of silver, according to the shekel of the sanctuary (that is, twenty gerahs). ¹⁷ But the firstborn of a cow, or the firstborn of a sheep, or the firstborn of a goat, you shall not redeem; they are holy. You shall dash their blood on the altar, and shall turn their fat into smoke as an offering by fire for a pleasing odor to the Lord;