1 Chronicles 23:3, 24-27

The Levites thirty years old and upward were counted, and their number man by man was 38,000.

These were the Levites by their fathers’ households, the heads of the fathers’ households of those registered, according to the number of names of the individuals who were the servants of the house of the LORD, from twenty years old and upward. For David said, “The LORD God of Israel, has given peace and rest to His people, and He dwells in Jerusalem forever. Also, the Levites will no longer need to carry the tabernacle and all its utensils for its service.” For by the last words of David, the Levites from twenty years old and above were counted.