Numbers 18:14

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

The first-ripe fruits of all that is in their land, which they bring to Yahweh, shall be yours; everyone who is clean in your house shall eat of it.

Everything that opens the womb, of all flesh which they offer to Yahweh, 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.

You shall redeem those who are to be redeemed of them from a month old, according to your estimation, for five shekels of money, after the shekel of the sanctuary (the same is twenty gerahs).