Michael Fitzgerald and Moulay Slitine, The Invocation of God, Islamic Texts Society, Introduction. стр. 4 (quoting Ibn Qayyim al-Jawziyya, Madarij al-Salikin fi ma bayna iyyaka na'budu wa iyyaka nasta'in, ed. Ahmad Fakhri al-Rifi and Asam Faris al-Hurstani, Beirut, Dar al-Jil, 1412/1991, II,. 41 and III. 431). Also, Ovamir Anjum, University of Toledo, Ohio, Sufism without Mysticism: Ibn al-Qayyim's Objectives in Madarij al-Salikin pp. 164 (https://www.academia.edu/2248220/Sufism_without_Mysticism_Ibn_al Qayyims_Objectives_in_Madarij_al-Salikin)
iranicaonline.org
S. de Laugier de Beaureceuil, "Abdullah Ansari" in Encylcoapedia Iranica [1]
