Exodus 13:15

13:15 When Pharaoh stubbornly refused to release us, the Lord killed all the firstborn in the land of Egypt, from the firstborn of people to the firstborn of animals. That is why I am sacrificing to the Lord the first male offspring of every womb, but all my firstborn sons I redeem.’

Numbers 3:45-51

3:45 “Take the Levites instead of all the firstborn males among the Israelites, and the livestock of the Levites instead of their livestock. And the Levites will be mine. I am the Lord. 3:46 And for the redemption of the 273 firstborn males of the Israelites who exceed the number of the Levites, 3:47 collect five shekels for each one individually; you are to collect this amount in the currency of the sanctuary shekel (this shekel is twenty gerahs). 3:48 And give the money for the redemption of the excess number of them to Aaron and his sons.”

3:49 So Moses took the redemption money from those who were in excess of those redeemed by the Levites. 3:50 From the firstborn males of the Israelites he collected the money, 1,365 shekels, according to the sanctuary shekel. 3:51 Moses gave the redemption money to Aaron and his sons, according to the word of the Lord, as the Lord had commanded Moses.