The song is like in every episode, like around 11 mins in episode 20 of Magi: The Kingdom of Magic, and also 19:28 in episode 16. I think this song may be in *The Labyrinth of Magic too, but can't remember.
The song is like 3 flutes playing. It is so haunting and medieval sounding.
I'm sure it's an unreleased song on the soundtrack since I've already tried to find the song, and by doing so come to know of this.