Sunan Abi Dawud Book 36, Hadith 15
Nafi' said that Ibn 'Umar used to wear his signet-ring on his left hand.
The Prophet (ﷺ) 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".
I saw as-Salt ibn Abdullah ibn Nawfal ibn AbdulMuttalib wearing the signet-ring on his right small finger. I asked: What is this? He replied: I saw Ibn Abbas wearing his ring in this manner. He put its stone towards the upper part of his palm. Ibn Abbas also mentioned that the Messenger of Allah (ﷺ) used to wear his signet-ring in his manner.