Numbers 3:40-45
The Substitution for the Firstborn
3:40 Then the Lord said to Moses, “Number all the firstborn males of the Israelites from a month old and upward, and take the number of their names.
3:41 And take the Levites for me – I am the Lord – instead of all the firstborn males among the Israelites, and the livestock of the Levites instead of all the firstborn of the livestock of the Israelites.”
3:42 So Moses numbered all the firstborn males among the Israelites, as the Lord had commanded him.
3:43 And all the firstborn males, by the number of the names from a month old and upward, totaled 22,273.
3:44 Then the Lord spoke to Moses:
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.