Abu Dawud Book 29, Hadith Number 4208.

Chapter : Fashioning a seal in the form of a ring.

Narated By N/A : The tradition mentioned above has also been transmitted by Ibn ‘Umar through a different chain of narrators from the Prophet (PBUH). This version adds: They searched for it but could not find it. ‘Uthman then fashioned a silver-ring and engraved on it “Muhammad, the Apostle of Allah.” He used to wear it or stamp with it. (the narrator is doubtful)