1 Chronicles 23:3-6

The Levites, thirty years old and upward, were numbered, and the total was 38,000 men. “Twenty-four thousand of these,” David said, “shall have charge of the work in the house of the LORD, 6,000 shall be officers and judges, 4,000 gatekeepers, and 4,000 shall offer praises to the LORD with the instruments that I have made for praise.” And David organized them in divisions corresponding to the sons of Levi: Gershon, Kohath, and Merari.