Abu Dawud Book 29, Hadith Number 4217.

Chapter : Wearing the signet ring on the right hand or the left hand.

Narated By Abdullah ibn Abbas : Muhammad ibn Ishaq said: I saw al-Salt ibn Abdullah ibn Nawfal ibn Abdul Muttalib 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 Apostle of Allah (PBUH) used to wear his signet-ring in his manner.