An excellent review of the history of Islamic spirituality/mysticism and its relationship to the prayer manual Shaifah Al-Sajjadiyah (translated in English as the Psalms of Islam) of Imam Zain al-Abideen (AS)

Below are links to some of the works mentioned in the talk by Dr. Masterton:

Shaifah Al-Sajjadiyah (trans. William Chittick)

A Comparative Exploration of the Authority of the Awliya’ in the Shi’i and Sufi Traditions by Dr. Masterton

The Concept of Sainthood in Early Islamic Mysticism: Two Works by Al-Hakim al-Tirmidhi – An Annotated Translation with Introduction