1 Chronicles 9:33
"And these are the singers, chief of the fathers of the Levites, who remaining in the chambers were free: for they were employed in that work day and night."
Cross References (ranked by relevance)
Nehemiah 11:17
And Mattaniah the son of Micha, the son of Zabdi, the son of Asaph, was the principal to begin the thanksgiving in prayer: and Bakbukiah the second among his brethren, and Abda the son of Shammua, the son of Galal, the son of Jeduthun.
Ezra 7:24
Also we certify you, that touching any of the priests and Levites, singers, porters, Nethinims, or ministers of this house of God, it shall not be lawful to impose toll, tribute, or custom, upon them.