Numbers 8:23-26

And the LORD spake unto Moses, saying, This is it that belongeth unto the Levites: from twenty and five years old and upward they shall go in to wait upon the service of the tabernacle of the congregation: and from the age of fifty years they shall cease waiting upon the service thereof, and shall serve no more: 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.