Numbers 1:51-53

⁵¹And when the tabernacle is to go forward, the Levites shall take it apart; and when the tabernacle is to be stationary, the Levites shall set it up; but the stranger who cometh nigh shall be put to death.

⁵²And the sons of Israel shall encamp every man upon his own dwelling-place, and every man by his standard, according to their hosts.

⁵³But the Levites shall dwell round about the tabernacle of the testimony, that there may not be wrath upon the congregation of the sons of Israel; and the Levites shall watch the watching of the tabernacle of testimony.