When the Prophet ﷺ wanted to write to the Romans, his companions told him that they would not read any letter unless it was sealed. So the Prophet ﷺ had a silver ring made. It is as if I can still see its brilliance, and its inscription read, "Muhammad, Messenger of Allah ﷺ."In another narration, he wanted to write to Chosroes, Caesar, and the Negus.
لما أراد النبي ﷺ أن يكتب إلى الروم قالوا: أنهم لا يقرؤون كتابا إلا مختوما، فاتخذ النبي ﷺ خاتما من فضة كأني أنظر إلى وبيصه ونقشه محمد رسول الله ﷺ. وفي رواية: أراد أن يكتب إلى كسرى وقيصر والنجاشي.
Bukhari narrated it in the Chapter on Rulings (7162), and Muslim in the Chapter on Clothing and Adornment (2092:56), from Muhammad bin Bashshar, with Muslim adding Muhammad bin Muthanna as well, saying, Ghundar narrated to us, Shubah narrated to us, he said, I heard Qatada narrate from Anas bin Malik, and he related it. The other narration in Muslim comes through Khalid bin Qays, from Qatada, with the same wording.