Numbers 8:20-26 - The Levites Are Dedicated To The Lord
20 And Moses will do, and Aaron, and all the assembly of the sons of Israel, to the Levites according to all which Jehovah commanded Moses for the Levites; so to them did the sons of Israel. 21 And the Levites will be purified, and will wash their garments; and Aaron will lift them up, a lifting up before Jehovah; and Aaron will expiate for them to cleanse them. 22 And after this the Levites went to serve their service in the tent of appointment, before Aaron and before his sons: as Jehovah commanded Moses for the Levites, so to them did they.
23 And Jehovah will speak to Moses, saying, 24 This is that to the Levites: from the son of five and twenty years and above, and he came in to war the warfare in serving the tent of appointment 25 And from the son of fifty years, he shall turn back from the warfare of the service, and shall serve no more. 26 And he served with his brethren in the tent of appointment, to watch the watches, and he shall work no work. Thus shalt thou do to the Levites in their watches.