Numbers 4:2-4

King James Version

² Take the sum of the sons of Kohath from among the sons of Levi, after their families, by the house of their fathers,

³ From thirty years old and upward even until fifty years old, all that enter into the host, to do the work in the tabernacle of the congregation.

⁴ This shall be the service of the sons of Kohath in the tabernacle of the congregation, about the most holy things: