Numbers 3:12-14 Modern English Version (MEV)
12 I Myself have taken the Levites from among the children of Israel instead of all the firstborn that open the womb among the children of Israel. Therefore the Levites will be Mine 13 because all the firstborn are Mine, for on the day that I struck all the firstborn in the land of Egypt I set apart to Me all the firstborn in Israel, both man and beast. They will be Mine. I am the Lord.
A Census of the Levites
14 The Lord spoke to Moses in the Wilderness of Sinai, saying: