Numbers 3:11-13, 45

The LORD also said to Moses, “I am choosing the Levites from all the Israelites to take the place of all the firstborn children of Israel. The Levites will be mine, because the firstborn are mine. When you were in Egypt, I killed all the firstborn children of the Egyptians and took all the firstborn of Israel to be mine, both animals and children. They are mine. I am the LORD.”

“Take the Levites instead of all the firstborn sons of the Israelites, and take the animals of the Levites instead of the animals of the other people. The Levites are mine. I am the LORD.