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 (TR)
English reference (TR): Book 12, Hadith 97 (TR)
Arabic reference (TR): Book 13, Hadith 103 (TR)