Abu Dawud
Signet Rings
Book Number: 029 / Hadith Number: 4212
Narated By Iyas b. al-Harith al-Mu'aiqib quoting his grandmother : The signet-ring of the Prophet (pbuh) was of iron polished with silver. Sometimes it remained in my possession. Al-Mu'ayqib was in charge of the signet-ring of the Prophet (pbuh).