It is related from Hazrat Anas radiyallahu anhu that the Prophet of Allah sallallahu alaihe wasallam wore a ring on the right hand, and some people have also related from Hazrat Anas radiyallahu anhu that the Prophet of Allah sallallahu alaihe wasallam wore a ring on the left hand (PT)
English reference (PT): Book 12, Hadith 97 (PT)
Arabic reference (PT): Book 13, Hadith 103 (PT)