Until around the time of Imam al-Sadiq (as), the term 'Sufi' was not in regular use, and the few that used it as an appellation were of the Mu'tazili and Imami schools, not the Sunni Ash'ari or Maturidi schools, which now dominate the Sufi scene.

Sufism is an amalgamation of Islamic ideas and practices and others that have been integrated into it from spiritual traditions that existed prior to Islam expanding into wider territories.

I have written a paper on this in more detail, if you are interested. Please write to me at [email protected] and I can send it to you.