Sketch by Frithjof Schuon of Plains Indian man. Found on p. 160 of Images of Primordial and Mystic Beauty (Abodes, 1992).
Christentum – Islam: Ausblicke auf eine esoterisch Ökumene (e-Book)
In this work, Frithjof Schuon compares Christianity and Islam and also looks at confessions within these world religions: Protestantism, Orthodoxy, and Shiism.