BaMidbar (Numbers) 8:15-26
15“Thereafter the Levi’im shall come to serve the Tent of Meeting; you shall purify them and you shall wave them as a wave-service. 16For presented are they to Me from among the Children of Yisra’el; in place of the first issue of every womb, the firstborn of everyone of the Children of Yisra’el, have I taken then to Myself. 17For every firstborn of the Children of Yisra’el became Mine, of man and livestock; on the day I struck every firstborn in the land of Egypt I sanctified them for Myself. 18I took the Levi’im in place of every firstborn among the Children of Yisra’el. 19Then I assigned the Levi’im to be presented to Aharon and his sons from among the Children of Yisra’el to perform the service of the Children of Yisra’el in the Tent of Meeting, and provide atonement for the Children of Yisra’el, so that there will not be a plaque among the Children of Yisra’el when the Children of Yisra’el approach the Sanctuary.”
20Moshe, Aharon, and the entire assembly of the Children of Yisra’el did to the Levi’im according to everything that HaShem had commanded Moshe about the Levi’im, so did the Children of Yisra’el do to them. 21The Levi’im purified themselves and immersed their garments; and Aharon waved them as a wave-service before HaShem, and Aharon provided atonement for them to purify them. 22Afterwards the Levi’im came to perform their services in the Tent of Meeting, before Aharon and before his sons, as HaShem commanded Moshe concerning the Levi’im; so they did for them.
23HaShem spoke to Moshe, saying, 24“This shall apply to the Levi’im: From twenty-five years of age and up, he shall join the legion of the service of the Tent of Meeting. 25From fifty years of age, he shall withdraw from the legion of work and no longer work. 26He shall minister with his brethren in the Tent of Meeting to safeguard the charge, but work shall he not perform. So shall you do to the Levi’im concerning their charge.”