Commentary for II Chronicles 35:15

וְהַמְשֹֽׁרֲרִ֨ים בְּנֵי־אָסָ֜ף עַל־מַעֲמָדָ֗ם כְּמִצְוַ֤ת דָּוִיד֙ וְאָסָ֞ף וְהֵימָ֤ן וִֽידֻתוּן֙ חוֹזֵ֣ה הַמֶּ֔לֶךְ וְהַשֹּׁעֲרִ֖ים לְשַׁ֣עַר וָשָׁ֑עַר אֵ֣ין לָהֶ֗ם לָסוּר֙ מֵעַ֣ל עֲבֹֽדָתָ֔ם כִּֽי־אֲחֵיהֶ֥ם הַלְוִיִּ֖ם הֵכִ֥ינוּ לָהֶֽם׃

And the singers the sons of Asaph were in their place, according to the commandment of David, and Asaph, and Heman, and Jeduthun the king’s seer; and the porters were at every gate; they needed not to depart from their service, for their brethren the Levites prepared for them.

Rashi on II Chronicles