Numbers 3:12, 40, 41

“I have taken the Levites from among the Israelites in place of the first male offspring of every Israelite woman. The Levites are mine

The LORD said to Moses, “Count all the firstborn Israelite males who are a month old or more and make a list of their names.

Take the Levites for me in place of all the firstborn of the Israelites, and the livestock of the Levites in place of all the firstborn of the livestock of the Israelites. I am the LORD.”