Sunan Abi Dawud Book 36, Hadith 4
The signet-ring of the Prophet (ﷺ) was all of silver as was also its stone.
The signet-ring of the Prophet (ﷺ) was of silver with an Abyssinian stone.
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.