Numbers 18:2-4

2Also bring with you your brethren of the tribe of Levi, the tribe of your father, that they may be joined with you and serve you while you and your sons are with you before the tabernacle of witness.

3They shall attend to your needs and all the needs of the tabernacle; but they shall not come near the articles of the sanctuary and the altar, lest they die—they and you also.

4They shall be joined with you and attend to the needs of the tabernacle of meeting, for all the work of the tabernacle; but an outsider shall not come near you.