1 Chronicles 23:2-5
2-5At the same time he brought together all the leaders of Israel, the priests, and the Levites. The Levites thirty years and older were counted; the total was thirty-eight thousand. David sorted them into work groups: "Twenty-four thousand are in charge of administering worship in the sanctuary; six thousand are officials and judges; four thousand are security guards; and four thousand are to serve in the orchestra, praising God with instruments that I have provided for praise." 6David then divided the Levites into groupings named after the sons of Levi: Gershon, Kohath, and Merari.