Numbers 3:40-41, 44-48

GOD spoke to Moses: “Count all the firstborn males of the People of Israel who are one month and older. List their names. Then set apart for me the Levites—remember, I am GOD—in place of all the firstborn among the People of Israel, also the livestock of the Levites in place of their livestock. I am GOD.”

Again GOD spoke to Moses. He said, “Take the Levites in place of all the firstborn of Israel and the livestock of the Levites in place of their livestock. The Levites are mine, I am GOD. Redeem the 273 firstborn Israelites who exceed the number of Levites by collecting five shekels for each one, using the Sanctuary shekel (the shekel weighing twenty gerahs). Give that money to Aaron and his sons for the redemption of the excess number of Israelites.”