Numbers 18:14

12 “I have given to you all the best of the oil, all the best of the vintage, and of the grain, the first fruits of them which they give to the LORD.

13 The first-ripe fruits of all that is in their land, which they bring to the LORD, shall be yours. Everyone who is clean in your house shall eat of it.

14 “Everything devoted in Israel shall be yours.

15 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.

16 You shall redeem those who are to be redeemed of them from a month old, according to your estimation, for five shekels of money, according to the shekel of the sanctuary, which weighs twenty gerahs.