Numbers 8:23-26

The LORD said to Moses, “This command is for the Levites. Everyone twenty-five years old or older must come to the Meeting Tent, because they all have jobs to do there. At the age of fifty, they must retire from their jobs and not work again. They may help their fellow Levites with their work at the Meeting Tent, but they must not do the work themselves. This is the way you are to give the Levites their jobs.”