The Concise Oxford Dictionary of World Religions (2359 page)

f
experience of absolute reality (
aq
qa
) is not opposed to shar
‘a but is its foundation.
The early history of Sufism is not yet clear. It seems to have emerged from a determination among some early Muslims not to be distracted by the rapid Muslim expansion over vast territories from the vision and practice of Mu
ammad in realizing the absolute sovereignty of God in life. Of this early attitude, al-
asan al-Ba
r
(Basra being an important centre of it) is a major example, and later S
f
orders look back to him as a key link in the connection back to the Prophet. Also from Basra was the notable Rabi‘a al-‘Adawiyya; but S
f
devotion took root in many different places, often absorbing in each place something of its different atmosphere. Thus Khuras
ni Sufism reflected its parched surroundings in an austere asceticism, producing such remembered figures as Fudayl ibn ‘Iyad,