Anas ibn Malik said: "The Prophet (Allah bless him and give him peace) wrote to Chosroes, Caesar and the Negus, whereupon he was told: 'The non-Arabs will not accept a letter unless it bears a seal.' Allah’s Messenger (Allah bless him and give him peace) therefore cast a signet which had a silver ring, and on which was engraved; “Muhammad is the Messenger of Allah.”