Sunan Abi Dawud Book 36, Hadith 6
He engraved on it "Muhammad, the Messenger of Allah." and said: "No one must engrave anything in the manner of this signet-ring of mine. He then transmitted the rest of the tradition.
The Messenger of Allah (ﷺ) took a signet-ring of gold, and put the stone next the palm of his hand. He engraved on it "Muhammad, the Messenger of Allah". The people then took signet-rings of gold. When he saw that they had taken them (like his ring) he threw it away and said: I shall never wear it. He then fashioned a silver ring and engraved on it "Muhammad, the Messenger of Allah". Then Abu Bakr wore it after him, then 'Umar wore it after Abu Bakr, and the 'Uthman wore it after 'Umar till it fell down in a well called Aris.
Abu Dawud said: The people did not disagree on 'Uthman till the signet-rin fell down from his hand.
They searched for it but could not find it. 'Uthman then fashioned a signet-ring and engraved on it "Muhammad, the Messenger of Allah". He used to wear it or stamp with it.