1 Chronicles 23:8 (KJV)

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.

The sons of Shimei; Shelomith, and Haziel, and Haran, three. These were the chief of the fathers of Laadan.

And the sons of Shimei were, Jahath, Zina, and Jeush, and Beriah. These four were the sons of Shimei.

And Jahath was the chief, and Zizah the second: but Jeush and Beriah had not many sons; therefore they were in one reckoning, according to their father's house.

The sons of Kohath; Amram, Izhar, Hebron, and Uzziel, four.

The sons of Amram; Aaron and Moses: and Aaron was separated, that he should sanctify the most holy things, he and his sons for ever, to burn incense before the LORD, to minister unto him, and to bless in his name for ever.