Exodus 13:2
"Consecrate to Me every firstborn male. The firstborn from every womb among the Israelites belongs to Me, both of man and beast."

Numbers 3:11
Again the LORD spoke to Moses, saying,

Numbers 3:41
You are to take the Levites for Me--I am the LORD--in place of all the firstborn of Israel, and the livestock of the Levites in place of all the firstborn of the livestock of the Israelites."

Numbers 3:45
"Take the Levites in place of all the firstborn of Israel, and the cattle of the Levites in place of their cattle. The Levites belong to Me; I am the LORD.

Numbers 8:14
In this way you shall separate the Levites from the rest of the Israelites, and the Levites will belong to Me.

Numbers 8:16
For the Levites have been wholly given to Me from among the sons of Israel. I have taken them for Myself in place of all who come first from the womb, the firstborn of all the sons of Israel.

Numbers 18:6
Behold, I Myself have selected your fellow Levites from the Israelites as a gift to you, dedicated to the LORD to perform the service for the Tent of Meeting.