Numbers 8:20-26 - The Levites Are Dedicated To The Lord
20 And Moses and Aaron and all the congregation of the sons of Israel did to the Levites according to all that Jehovah commanded Moses concerning the Levites. So the sons of Israel did to them. 21 And the Levites purified themselves, and they washed their clothes. And Aaron offered them, an offering before Jehovah. And Aaron made an atonement for them to purify them. 22 And after that the Levites went in to do their service in the tabernacle of the congregation before Aaron and before his sons. Even as Jehovah had commanded Moses concerning the Levites, so they did to them.
23 And Jehovah spoke to Moses saying, 24 This is that which pertains to the Levites. From twenty-five years old and upward they shall go in to wait upon the service of the tabernacle of the congregation. 25 And from the age of fifty years they shall stop waiting upon the service, and shall serve no more. 26 But they shall minister with their brothers in the tabernacle of the congregation, to keep the charge; only he shall not serve at a service. So you shall do to the Levites as to their duties.