I Chronicles 23:3-6:
Now the Levites were numbered from the age of thirty years and upward: and their number by their polls, man by man, was thirty and eight thousand. Of which, twenty and four thousand were to set forward the work of the house of the LORD; and six thousand were officers and judges: Moreover four thousand were porters; and four thousand praised the LORD with the instruments which I made, said David, to praise therewith. And David divided them into courses among the sons of Levi, namely, Gershon, Kohath, and Merari.
II Chronicles 7:5-6:
And king Solomon offered a sacrifice of twenty and two thousand oxen, and an hundred and twenty thousand sheep: so the king and all the people dedicated the house of God. And the priests waited on their offices: the Levites also with instruments of musick of the LORD, which David the king had made to praise the LORD, because his mercy endureth for ever, when David praised by their ministry; and the priests sounded trumpets before them, and all Israel stood.
II Chronicles 29:25-26:
And he set the Levites in the house of the LORD with cymbals, with psalteries, and with harps, according to the commandment of David, and of Gad the king’s seer, and Nathan the prophet: for so was the commandment of the LORD by his prophets. And the Levites stood with the instruments of David, and the priests with the trumpets.