Sahih Bukhari Volume 007, Book 072, Hadith Number 766.

Narrated By Anas bin Malik  : Allah's Apostle took a silver ring and had 'Muhammad, the Apostle' of Allah' engraved on it. The Prophet then said (to us), 'I have a silver ring with 'Muhammad, the Apostle of Allah engraved on it, so none of you should have the same engraving on his ring."