Numbers 1:47-50

⁴⁷But the Levites in the tribes of their families were not numbered with them.

⁴⁸And the Lord spoke to Moses, saying:

⁴⁹Number not the tribe of Levi, neither shalt thou put down the sum of them with the children of Israel:

⁵⁰But appoint them over the tabernacle of the testimony, and all the vessels thereof, and whatsoever pertaineth to the ceremonies. They shall carry the tabernacle and all the furniture thereof: and they shall minister, and shall encamp round about the tabernacle.