The Third Priest's Tale

Japanese ghost story. A young boy finds a wooden flute inside his father's armor. The father sends his son off to learn how to play, and upon his return, the boy plays the same song the father heard when he was at war.  He killed the flute player, who was the enemy and brought back the flute. Years later, the son has become a priest. When he was asked if he played the flute, he responded no. He wasn't sure where the music came from.