Although well-known for his love and care for creation, his life of simplicity and the Catholic order that now bears his name; Francis also has much to offer Muslim-Christian relations in his less well-known encounter with the Sultan of Egypt.
The main sources on Francis’ visit to al-Kamil are Jacque de Vitry’s letter from Damietta (1220, Early Documents, vol I, pp. 580-581) and Historia Orientalis (1221-5, vol I, pp. 582-585); Thomas de Celano’s The Life of Francis (1228-9, vol I, pp. 229-231) and Bonaventure’s Major Legend of St Francis (1260-1263, vol II, pp. 602-604).
Very relevant is chapter 16 of Francis’ Regula Non Bullata, (1221), which gives instructions for friars who wish to preach to Muslims.
The accounts conflict, and most have hagiographic elements. A helpful analysis of the various sources and ways of interpreting them is in De Beer, F., ‘St Francis and Islam’, in F. McDonagh (trans), C. Duquoc and C. Floristan (eds), ‘St Francis today’, Concilium 149, NY: Sowbury Press, 1979, pp. 11-20.
A different analysis of the primary sources and their development is in “Francis of Assisi before the Sultan: Islam in Early Franciscan Writings (1219-1267)”, R. W. Lawrence, 2008, available via www.amss.org (Scroll down to final papers.)
C.A. Mallouhi, Waging Peace on Islam (Monarch, 2000) offers a helpful and moving reconstruction of events that has the great advantage of taking the Muslim accounts of al-Kamil seriously.
J. Hoeberichts, Francis and Islam (Illinois: Franciscan Press, 1997) offers an analysis not only of Francis’ visit to al-Kamil but also of chapter 16 of the Regula Non Bullata in its wider context.
B.Z. Kedar, Crusade and Mission (Princeton: Princeton University Press, 1984), explores the links between mission to Muslims and the Crusades in medieval thinking. Chapter 3 compares Francis and Jacques de Vitry.