Numbers 3:12-13

“I myself receive the Levites from the midst of the Israelites in the place of all the firstborn of the offspring of the womb from the Israelites. The Levites will be mine because all the firstborn are mine; on the day of my killing all the firstborn in the land of Egypt, I consecrated for myself all the firstborn in Israel, both humankind and animal; they will be mine. I am Yahweh.”