Numbers 3:6-13
6 “Bring the tribe of Levi and present them to Aaron the priest to assist him.
7 They are to perform duties for him and for the whole community at the Tent of Meeting by doing the work of the tabernacle.
8 They are to take care of all the furnishings of the Tent of Meeting, fulfilling the obligations of the Israelites by doing the work of the tabernacle.
9 Give the Levites to Aaron and his sons; they are the Israelites who are to be given wholly to him.
10 Appoint Aaron and his sons to serve as priests; anyone else who approaches the sanctuary must be put to death.”
11 The Lord also said to Moses,
12 “I have taken the Levites from among the Israelites in place of the first male offspring of every Israelite woman. The Levites are mine,
13 for all the firstborn are mine. When I struck down all the firstborn in Egypt, I set apart for myself every firstborn in Israel, whether man or animal. They are to be mine. I am the Lord.”