Numbers 18:2-3

²Bring your brothers also, the tribe of Levi, the tribe of your father, near with you, that they may be joined to you, and minister to you; but you and your sons with you shall be before the Tent of the Testimony.

³They shall keep your commands and the duty of the whole Tent; only they shall not come near to the vessels of the sanctuary and to the altar, that they not die, neither they nor you.