Anas bin Malik (RA) reported that when Allah's Messenger (ﷺ) decided to write letters to the Byzantine (Emperor) they (his Companions) told him that they would not read a letter unless it is sealed. (Then) Allah's Messenger (ﷺ) had a silver ring made (for himealf), (its shape is too vivid in my mind) as if I see its brightness in the band of Allah's Messenger (ﷺ) and its engravement was (Muhammad, Messenger of Allah) (ﷺ) .
Hadith Referenceصحيح مسلم / كتاب اللباس والزينة / 2092
Anas reported that when Allah's Apostle (ﷺ) decided to write (letters) to non-Arabs (i. e. Persian and Byzantine Emperors) it was said to him that the non-Arabs would not accept a letter but that having a seal over it; so he (the Holy Prophet) got a silver ring made. He (Anas) said: I perceive as if I am looking at its brightness in his hand.
Hadith Referenceصحيح مسلم / كتاب اللباس والزينة / 2092
Anas reported that when Allah's Apostle (ﷺ) decided to write to the Kisri (the King of Persia), Caesar (Emperor of Rome), and the Negus (the Emperor of Abyssinia), it was said to him that they would not accept the letter without the seal over it; so Allah's Messenger (ﷺ) got a seal made, the ring of which was made of silver and there was engraved on it. (Muhammad. the Messenger of Allah) (ﷺ) .
Hadith Referenceصحيح مسلم / كتاب اللباس والزينة / 2092