Sufism originated from the ancient school of Egyptian mysteries, a school which existed even before Abraham, the father of three great religions: Christianity, Judaism, and Islam. Those who know Sufism from superficial writings, and, sometimes, from translations of the Arabic or Persian literature, are apt to think that Sufism is the mystical side of Islam. In reality, it is not true. Sufism existed before Mohammed, before Jesus Christ, before Abraham.

It is true that the mystics in the world of Islam are called Sufis, but that does not mean that "Sufi" means the mystics of Islam. For instance, the green color is the national color of the Irish, but that does not mean that everybody who dresses in green is from Ireland. The green color existed even before people inhabited Ireland.

http://www.appliedmeditation.org/About_IAM/Sufism.shtml