Numbers 3:6-16

6Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister unto him. 7And they shall keep his charge, and the charge of the whole congregation before the tent of meeting, to do the service of the tabernacle. 8And they shall keep all the furniture of the tent of meeting, and the charge of the children of Israel, to do the service of the tabernacle. 9And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him on the behalf of the children of Israel. 10And thou shalt appoint Aaron and his sons, and they shall keep their priesthood: and the stranger that cometh nigh shall be put to death.

11And Jehovah spake unto Moses, saying, 12And I, behold, I have taken the Levites from among the children of Israel instead of all the first-born that openeth the womb among the children of Israel; and the Levites shall be mine: 13for all the first-born are mine; on the day that I smote all the first-born in the land of Egypt I hallowed unto me all the first-born in Israel, both man and beast; mine they shall be: I am Jehovah.

14And Jehovah spake unto Moses in the wilderness of Sinai, saying, 15Number the children of Levi by their fathers’ houses, by their families: every male from a month old and upward shalt thou number them. 16And Moses numbered them according to the word of Jehovah, as he was commanded.