Numbers 18:2-3

²And also thy brethren, the tribe of Levi, the tribe of thy father, bring thou near with thee, that they may be joined with thee, and minister unto thee; while thou and thy sons with thee shall be before the tabernacle of the testimony.

³And they shall keep thy charge, and the charge of all the tabernacle: only unto the vessels of the sanctuary and unto the altar shall they not come near, that they may not die, either they or you.