Numbers 8:16-18

King James Version

¹⁶ For they are wholly given unto me from among the children of Israel; instead of such as open every womb, even instead of the firstborn of all the children of Israel, have I taken them unto me.

¹⁷ For all the firstborn of the children of Israel are mine, both man and beast: on the day that I smote every firstborn in the land of Egypt I sanctified them for myself.

¹⁸ And I have taken the Levites for all the firstborn of the children of Israel.