Numbers 18:2-4

ASV_Strongs(i)
  2 H251 And thy brethren H4294 also, the tribe H3878 of Levi, H4294 the tribe H1 of thy father, H7126 bring H3867 thou near with thee, that they may be joined H8334 unto thee, and minister H1121 unto thee: but thou and thy sons H6440 with thee shall be before H168 the tent H5715 of the testimony.
  3 H8104 And they shall keep H4931 thy charge, H4931 and the charge H168 of all the Tent: H7126 only they shall not come nigh H3627 unto the vessels H6944 of the sanctuary H4196 and unto the altar, H4191 that they die not, neither they, nor ye.
  4 H3867 And they shall be joined H8104 unto thee, and keep H4931 the charge H168 of the tent H4150 of meeting, H5656 for all the service H168 of the Tent: H2114 and a stranger H7126 shall not come nigh unto you.