Numbers 1:47-50

47But the Levites after the tribe of their fathers were not numbered among them. 48For Yhwh had spoken unto Moses, saying, 49Only thou shalt not number the tribe of Levi, neither take the sum of them among the children of Israel: 50But thou shalt appoint the Levites over the tabernacle of testimony, and over all the vessels thereof, and over all things that belong to it: they shall bear the tabernacle, and all the vessels thereof; and they shall minister unto it, and shall encamp round about the tabernacle.