Numbers 3:41-45

The Levites must be reserved for me as substitutes for the firstborn sons of Israel; I am the LORD. And the Levites’ livestock must be reserved for me as substitutes for the firstborn livestock of the whole nation of Israel.” So Moses counted the firstborn sons of the people of Israel, just as the LORD had commanded. The number of firstborn sons who were one month old or older was 22,273. Then the LORD said to Moses, “Take the Levites as substitutes for the firstborn sons of the people of Israel. And take the livestock of the Levites as substitutes for the firstborn livestock of the people of Israel. The Levites belong to me; I am the LORD.