Numbers 8:16-18
16 For they have been exclusively assigned to Me from the Israelites.(A) I have taken them for Myself in place of all who come first from the womb, every Israelite firstborn.(B)
17 For every firstborn among the Israelites is Mine, both man and animal. I consecrated them to Myself(C) on the day I struck down every firstborn in the land of Egypt.
18 But I have taken the Levites in place of every firstborn among the Israelites.