Numbers 8:16-18 New English Translation (NET Bible)
16 For they are entirely given[a] to me from among the Israelites. I have taken them for myself instead of[b] all who open the womb, the firstborn sons of all the Israelites. 17 For all the firstborn males among the Israelites are mine, both humans and animals; when I destroyed[c] all the firstborn in the land of Egypt I set them apart for myself. 18 So I have taken the Levites instead of all the firstborn sons among the Israelites.