Rumi loved music so much. In his poetry, he often marries music with words and vice versa. One of the most famous music instruments that he repeatedly mentions in his poetry is "flute." Flute was the most handy, and attainable instrument in his time. No matter, it was played by a goatherd in the desert, or, by a lad in the court, it sounded the same to a mystic, like Maulana Jalaluddin Rumi. For he has heard it, breathed it, and felt the sorrowful feelings of a lover, to the point that in one of his ballads, he says:
"We have fallen into the place
where everything is music."
Translated by Coleman Barks
Among other musical instruments, Rabab was one of them that Rumi loved it so much. Rabab was one of the main instruments that was played in Khanqah (the Sufi lodges). Up to the present time, Rabab remains an influential instrument in Khanqahs, and other Sufi gatherings in Afghanistan.
He probably liked Rabab because of its rhythmic sounds. Rabab produced the sound of ecstasy, when its sounds reach the ceiling, it echoed throughout the lodge, and a melody of ecstasy reverberated through the souls of Sufis. Then, they were not in themselves, they were floating over the sounds of Rabab, and went beyond what they called the mystical ecstasy.
Rumi, in his words talks about the influence of sounds of Rabab, as follows:
"Do you know what the voice of the rabab is saying?
Come follow in my steps and find the way;
Since through error you’ll discover what’s right,
Since through questions you’ll end up with answers."
Source of translation is unknown, but I got it from here