Numbers 18:15

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.

Numbers 18:15 In-Context

13 The first fruits of all that is in their land, which they bring to the Lord, shall be yours; everyone who is clean in your house may eat of it.
14 Every devoted thing in Israel shall be yours.
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;
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.