The seal of the Prophet ﷺ was made of iron with silver wound around it. He said, "Sometimes it was in my hand," for Muqayqib was in charge of the seal of the Messenger of Allah ﷺ.
أخبرنا عمرو بن علي عن أبي عتاب سهل بن حماد ح وأنبأنا أبو داود حدثنا أبو عتاب سهل بن حماد قال حدثنا أبو مكين قال
كان خاتم النبي ﷺ حديدا ملويا عليه فضة قال وربما كان في يدي فكان معيقيب على خاتم رسول الله ﷺ
No references are available.
[Its chain of transmission is hasan] Abu Dawud narrated it in the chapter on the iron ring, in the section on what has been said about the iron ring, hadith no. 4224, from the hadith of Sahl bin Hammad through this route. It is also found in Kubra, no. 9531.