Numbers 8:23-25

Young's Literal Translation

²³ And Jehovah speaketh unto Moses, saying,

²⁴ `This [is] that which [is] the Levites': from a son of five and twenty years and upward he doth go in to serve the host in the service of the tent of meeting,

²⁵ and from a son of fifty years he doth return from the host of the service, and doth not serve any more,