Numbers 3:12-13

Behold, I have taken the Levites from among the Israelites instead of every firstborn who opens the womb among the Israelites; and the Levites shall be Mine, For all the firstborn are Mine. On the day that I slew all the firstborn in the land of Egypt, I consecrated for Myself all the firstborn in Israel, both man and beast; Mine they shall be. I am the Lord.