1 Chronicles 23:4, 24

“Twenty-four thousand of these,” David said, “shall have charge of the work in the house of the LORD, 6,000 shall be officers and judges

These were the sons of Levi by their fathers’ houses, the heads of fathers’ houses as they were listed according to the number of the names of the individuals from twenty years old and upward who were to do the work for the service of the house of the LORD.