Numbers 8:26 in the King James Version
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.
Context
25 and from the age of fifty years they shall retire from doing the work, and shall serve no more,
26 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.”