This book explores the profound spiritual encounter between Serge de Beaurecueil (1917-2005), a twentieth-century French Dominican friar and Christian mystic, and the eleventh-century Ḥanbalī Sufi master Khwāja 'Abdullāh Anṣārī of Herāt (1006-1089). De Beaurecueil lived much of his Christian discipleship in Cairo and Afghanistan, where he became the foremost expert on the life and thought of Anṣārī. His mystical conversation and scholarly engagement with Anṣārī, his experience of Islamic hospitality, and the transformation of his own practical spirituality or praxis mystica through his experience of dwelling in the abode of Islam provide us with not only a magnificent and luminous meditation on the hidden and abiding presence of God among Muslims but also a contemplation on the quandary of genuine engagement with and openness to the religious other.