Numbers 8:26

And his brother shall serve in the tabernacle of witness to keep charges, but he shall not do works: so shalt thou do to the Levites in their charges.

But shall minister with their brethren in the tabernacle of the congregation, to keep the charge, and shall do no service. Thus shalt thou do unto the Levites touching their charge.

but shall assist their brothers in the Tent of Meeting, to perform the duty, and shall perform no service. This is how you shall have the Levites do their duties.”