Numbers 18:2-3

²And take with thee thy brethren also of the tribe of Levi, and the sceptre of thy father, and let them be ready in hand, and minister to thee: but thou and thy sons shall minister in the tabernacle of the testimony.

³And the Levites shall watch to do thy commands, and about all the works of the tabernacle: only they shall not come nigh the vessels of the sanctuary nor the altar, lest both they die, and you also perish with them.