I was wondering if there are any primary sources on the letter that the Mongol Khan Hulagu wrote to the Mamluk Sultan Qutuz (from Wikipedia: "Hulagu intended to continue southward through Palestine towards Cairo to fight the Mamluks. He sent a threatening letter to the Mamluk Sultan Qutuz in Cairo. He demanded that Qutuz open Cairo or it would be destroyed like Baghdad.") Everywhere I looked they didn't give a concrete source, is there maybe the letter preserved or maybe a transcript written during that time? Thanks.
I believe that this is John Woods' translation of Rashid al-Din Fazlallah 'Conquest of Bagdad'. (quoted at Conquest of Baghdad (1258) by Rashid al-Din Fazlallah (d. 1318)).
It should be noted that Rashid-al-Din Hamadani was a Jewish Muslim working for the Ilkhanids and also their Grand vizier before he was executed. So it is a moot point as to whether he ever actually saw the original letter, of which no copies exist, made it up entirely, 'improved' the original or a copy, or embroidered tales that he had heard for political impact.
You can read the original here, and it is worth taking just a few minutes as it is a beautiful example of medieval illustrated calligraphy.