Numbers 8:22-26

Thomson(i) 22 and, after this, the Levites had gone in to perform their service in the tabernacle of the testimony, in the presence of Aaron and his sons; when they had done thus for the Levites, as the Lord had commanded Moses in respect to them; 23 then the Lord spoke to Moses, saying, 24 There is this further in respect to the Levites; from twenty five years and upwards, they shall go in to perform service at the tabernacle of the testimony; 25 but after fifty years of age, they are to be withdrawn from the service, and work no more. 26 As brothers, they are to keep watch at the tabernacle of the testimony, but not to perform laborious work. In this manner thou shalt dispose of the Levites among their watches.