Abu Dawud Book 29, Hadith Number 4215.
Chapter : Wearing the signet ring on the right hand or the left hand.
Narated By Abdullah ibn Umar : The Prophet (PBUH) used to wear the signet-ring on his left hand, and put its stone next the palm of his hand.
Abu Dawud said: Ibn Ishaq and Usamah b. Zaid transmitted from Nafi’: “on his right hand.”