Numbers 18:15 in the World English Bible
Everything that opens the womb, of all flesh which they offer to the LORD, both of man and animal, shall be yours. Nevertheless, you shall surely redeem the firstborn of man, and you shall redeem the firstborn of unclean animals.
Context
14 Every thing devoted in Israel shall be thine.
15 Every thing that openeth the matrix in all flesh, which they bring unto the LORD, whether it be of men or beasts, shall be thine: nevertheless the firstborn of man shalt thou surely redeem, and the firstling of unclean beasts shalt thou redeem.
16 And those that are to be redeemed from a month old shalt thou redeem, according to thine estimation, for the money of five shekels, after the shekel of the sanctuary, which is twenty gerahs.