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By the eleventh century, Sufism evolved into a well-developed movement with a body of literature on Quranic studies and Sufi practices. Institutionally, the sufis began to organise communities around the hospice or Khanqah controlled by a teaching master known as shaikh. He enrolled disciples and appointed a successor. He established rules for spiritual conduct and interaction between inmates as well as between laypersons and the master. Sufi silsilas began to crystallise in different parts of the Islamic world around the twelfth century.