Anas ibn Malik · Signet-Rings (Kitab Al-Khatam)

It remained in his hand until he died, in the hand of 'Abu Bakr until he died, in the hand of 'Umar until he died, and in the hand of 'Uthman. When he was near a well, it fell down in it. He ordered to take it out, but it could not be found.

The signet-ring of the Prophet (ﷺ) was of silver with an Abyssinian stone.

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.