1 Chronicles 23:3-7

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.

Of the Gershonites were, Laadan, and Shimei.