Hazrat Ibn Umar radiallahu anhu says that Rasulullah sallallahu alayhe wasallam had a ring made of silver. He used it as a seal (Stamp) on letters etc., but did not wear it (RU)
English reference (RU): Book 11, Hadith 83 (RU)
Arabic reference (RU): Book 12, Hadith 88 (RU)