Numbers 8:17-19

Amplified Bible, Classic Edition

¹⁷ For all the firstborn of the Israelites are Mine, both of man and beast; on the day that I smote every firstborn in the land of Egypt [not of Israel], I consecrated them and set them apart for Myself.

¹⁸ And I have taken the Levites instead of all the firstborn of the Israelites.

¹⁹ And I have given the Levites as a gift to Aaron and to his sons from among the Israelites to do the service of the Israelites at the Tent of Meeting and to make atonement for them, that there may be no plague among the Israelites if they should come near the sanctuary.