Leviticus 27:26-27 - Redemption Of The Firstborn
26 Only the firstling of the animals, which should be the LORD'S firstling, no man may dedicate it; whether it be ox, or sheep: it is the LORD'S. 27 And if it be of an unclean animal, then he shall redeem it according to your valuation, and shall add a fifth part to it: or if it be not redeemed, then it shall be sold according to your valuation.
40 And the LORD said unto Moses, Number all the firstborn of the males of the children of Israel from a month old and upward, and take the number of their names. 41 And you shall take the Levites for me (I am the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel. 42 And Moses numbered, as the LORD commanded him, all the firstborn among the children of Israel. 43 And all the firstborn males according to the number of names, from a month old and upward, of those that were numbered of them, were twenty and two thousand two hundred and threescore and thirteen.
44 And the LORD spoke unto Moses, saying, 45 Take the Levites instead of all the firstborn among the children of Israel, and the cattle of the Levites instead of their cattle; and the Levites shall be mine: I am the LORD.
46 And for those that are to be redeemed of the two hundred and threescore and thirteen of the firstborn of the children of Israel, who are more than the Levites; 47 You shall even take five shekels apiece individually, after the shekel of the sanctuary shall you take them: (the shekel is twenty gerahs:) 48 And you shall give the money, with which the excess number of them is to be redeemed, unto Aaron and to his sons.
49 And Moses took the redemption money of them that were over and above them that were redeemed by the Levites: 50 Of the firstborn of the children of Israel took he the money; a thousand three hundred and threescore and five shekels, according to the shekel of the sanctuary: 51 And Moses gave the money of them that were redeemed unto Aaron and to his sons, according to the word of the LORD, as the LORD commanded Moses.