Numbers 3:45-48

“Take the Levites instead of all the firstborn among the children of Israel, and the livestock of the Levites instead of their livestock. The Levites shall be Mine: I am the LORD. And for the redemption of the two hundred and seventy-three of the firstborn of the children of Israel, who are more than the number of the Levites, you shall take five shekels for each one individually; you shall take them in the currency of the shekel of the sanctuary, the shekel of twenty gerahs. And you shall give the money, with which the excess number of them is redeemed, to Aaron and his sons.”