Sufism-The Mysticism of Islam by Reynold A Nicholson

Sufism, the religious philosophy of Islam, is described in the oldest extant definition as the apprehension of divine realities, and Muhammadan mystics are fond of calling themselves Ahl al-Haqq, 'the followers of the Real.' Here, a sketch is drawn in broad outline on certain principles, methods, and characteristic features of the inner life as it has been lived by Muslims of every class and condition from the eighth century, of our era to the present day...
The Sufi who sets out to seek God calls himself a 'traveller' (salik); he advances by slow 'stages' (maqamat) along a 'path' (tariqat) to the goal of union with Reality...

Publisher - Gulshan Books