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 (RU)
English reference (RU): Book 12, Hadith 94 (RU)
Arabic reference (RU): Book 13, Hadith 100 (RU)