Numbers 18:2-3

²And thy brethren also of the tribe of Levi, the tribe of thy father, bring with thee, and let them be added with thee, to serve thee; but thou and, thy sons with thee (shall minister) before the tabernacle of the testimony.

³And they shall keep thy charge, and the charge of all the tabernacle; but to the vessels of the sanctuary and of the altar they (the Levites) shall not approach, that neither they nor you may die.