The Messenger of Allah (PBUH) made a ring of silver and it was on his hand, then it was on Abu Bakr’s hand after him, then it was on 'Umar’s hand, then it was on 'Uthman’s hand, and it was engraved: Muhammad the Messenger of Allah.
The Messenger of Allah (PBUH) had a ring of gold and he would place its stone towards his palm. Then people started to wear gold rings too. So he put it away and made a ring of silver.
The Prophet's ring was on this and he pointed to the little finger of his left hand.