English Translation
Narrated Anas bin Malik: When the Prophet intended to write to the Byzantines, it was said to him, "Those people do not read your letter unless it is stamped." So the Prophet took a silver ring and got 'Muhammad, the Apostle of Allah' engraved on it .... as if I am now looking at its glitter in his hand.
This hadith is from Sahih al-Bukhari, the most rigorously authenticated collection in Islamic scholarship. No editorial opinion is added.