Shama-il Tirmidhi Chapter 12, Hadith Number 5 (94).

Salt bin Abdullah says that Hazrat Ibn Abbas radiyallahu anhu wore a ring on the right hand, and as far as I can remember he used to say that the Prophet of Allah sallallahu alaihe wasallam also wore it on the right hand.

Commentary.
Imam Tirmizi has written this hadith briefly. It is mentioned with more detail in the Abu Daud. Ibn Ishaq says, “I have seen Salt wear a ring on the smallest finger of his right hand (this is known as the chungla finger in Urdu). I enquired the reason from him. He replied, “I have seen Hazrat Ibn Abbas radiyallahu anhu wearing it in this manner. The top part of the ring was facing outwards, as far as I can recall he was talking about the Prophet of Allah sallallahu alaihe wasallam and said that the Prophet of Allah sallallahu alaihe wasallam wore it in the same manner.”

Two things are mentioned in this hadith. One is that the top part was kept on the outer side of the finger. It is stated in the ‘Badh-lul-Majhud’ and ‘Mirqaatus-Su’ud’ that it is more correct to wear the top part of the ring facing the inside (towards the palms). This has also been stated in many narrations. This is also mentioned in the hadith appearing hereafter. Allamah Munaawi says that this is best because it protects the stone and saves one from pride and high mindedness. The second matter referred to is the wearing of the ring on the smallest finger. Imam Nawawi says that it is sunnah to do so according to the Ijmaa’. Allamah Shaami states that the ring should be on this finger, and the stone should face towards the palm for men, and towards the outside for women, as they wear it for beauty and elegance.