Sahih Bukhari Volume 007, Book 072, Hadith Number 762.

Narrated By Ibn 'Umar : Allah's Apostle had a silver ring made for himself and it was worn by him on his hand. Afterwards it was worn by Abu Bakr, and then by 'Umar, and then by 'Uthman till it fell in the Aris well. (On that ring) was engraved: 'Muhammad, the Apostle of Allah."