edited by, Frank Gaynor
Philosophical Library, 1953
Buku Referensi
Nicholson, Reynold A. (Reynold Alleyne), author
University Press , 1967
Buku Teks
Al-Attas, Syed Muhammad Naguib
Kuala Lumpur : University of Malay Press, 1970.
Buku Teks
Collins, John E. (John Edward), author
Rowman & Littlefield, 1991
Buku Teks
Khan, Hazrat Inayat
The Sufi International Headquarter's, 1956
Buku Teks