Persian Sufi Poetry, p. 73,
A Literary History of Persia, Vol. III, p. 141-146
Jan Rypka's History of Iranian Literature, p. 254
about Sufism
Abu l-Hasan 'Ali al-Hujwiri: Frasi in inglese
Kashf ul Mahjoob, Chapter I, Affirmation of Knowledge, p. 80
Kashf ul Mahjoob