דברי הימים א כה:א פירוש: רש״י

Then David separated for the service to sing the songs.

the sons of Asaph, etc. Out of all the Levites he separated only the sons of Asaph, etc.

Heman, and Jeduthun, who prophesied When they would play these musical instruments, they would prophesy. A similar incident [is told] of Elisha: (II Kings 3:15): “’And now fetch me a musician.’ And when the musician played, the hand of the Lord came upon him.”