1 Chronicles 23:4 KJV

2And he gathered together all the princes of Israel, with the priests and the Levites.

3Now 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.

4Of which, twenty and four thousand were to set forward the work of the house of the LORD; and six thousand were officers and judges:

5Moreover four thousand were porters; and four thousand praised the LORD with the instruments which I made, said David, to praise therewith.

6And David divided them into courses among the sons of Levi, namely, Gershon, Kohath, and Merari.