Henry Mackenzie (1815). “The Works of Henry Mackenzie, Esq. ...: The man of feeling, and miscellaneous pieces.-v.II. The man of the world.-v.III. Julia de Roubigné”, p.192
Khalid ibn al-Walid's letter to the Persian monarch Emperor Yazdegerd III, as quoted in John Clark Ridpath "History of the World, Volume IV (Book XII: The Mohammedan Ascendency, p. 463), 1910.