Sir Thomas Arnold, The Preaching ol Islam: A History of the Propagation of the Muslim Faith (2nd ed.; London: Constable & Co., 1913), p.88. The last paragraph is quoted from De Ludovici vii. itinere, in Jacques-Paul Migne, ed., Patrologia Cursus Completus: Series Latina (Paris, 1844-1864), CXCV, 1243.