Numbers 1:52-54

52And the children of Israel shall encamp every man in his camp, and every man by his own standard, according to their hosts; 53but the Levites shall encamp round about the tabernacle of testimony, that there come not wrath upon the assembly of the children of Israel; and the Levites shall keep the charge of the tabernacle of testimony. 54And the children of Israel did so; according to all that Jehovah had commanded Moses, so did they.