Numbers 18:2-7

²And thy brethren also of the tribe of Levi, the tribe of thy father, bring thou with thee, that they may be joined to thee, and minister to thee: but thou and thy sons with thee shall minister before the tabernacle of witness.

³And they shall keep thy charge, and the charge of all the tabernacle: only they shall not come nigh the vessels of the sanctuary and the altar, that neither they, nor ye also, die.

⁴And they shall be joined to thee, and keep the charge of the tabernacle of the congregation, for all the service of the tabernacle: and a stranger shall not come nigh to you.

⁵And ye shall keep the charge of the sanctuary, and the charge of the altar: that there be no wrath any more upon the children of Israel.

⁶And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are given as a gift for the LORD, to do the service of the tabernacle of the congregation.

⁷Therefore thou and thy sons with thee shall keep your priest's office for every thing of the altar, and within the vail; and ye shall serve: I have given your priest's office to you as a service of gift: and the stranger that cometh nigh shall be put to death.