1 Chronicles 23:5

So when David was old and full of days, he made Solomon his son king over Israel.

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

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: