The Persian Mystics: Jalalu'd-Din Rumi, Wisdom Of The East
by F. Hadland Davis
1912

...the Mohammedans Sufiism, or Persian mysticism, is known as tasawwuf. The word Sufi is derived from sui, meaning" wool." When a little Persian sect at the end of the eighth century A.D. broke away from the orthodox ~iuslhn religion, and struck out on an independent path, they ignored costly robes and worldly ostentation, and clad themselves in a white wool garment. Hence they were known as "wool wearers," or Sufis. Prof. Edward G. Browne gives four theories in regard to the origin of Sufiism...