For they are wholly given to Me from among the children of Israel; I have taken them for Myself instead of all who open the womb, the firstborn of all the children of Israel.
Numbers 8:16
Surrounding context
8:15 After that the Levites shall go in to service the tabernacle of meeting. So you shall cleanse them and offer them like a wave offering.
8:16 For they are wholly given to Me from among the children of Israel; I have taken them for Myself instead of all who open the womb, the firstborn of all the children of Israel.
8:17 For all the firstborn among the children of Israel are Mine, both man and beast; on the day that I struck all the firstborn in the land of Egypt I sanctified them to Myself.