Musnad Ahmad 27:917

'Affan narrated to us, Abu 'Awanah narrated to us, from Abu Bishr, from Nafi', from Ibn 'Umar, who said: "The Prophet, peace and blessings of Allah be upon him, had a ring of gold, and he used to place its stone on the inside of his palm." He said: "Then he cast it away one day, so the people cast away their rings. Then he took a ring of silver, and he used to seal with it, but he would not wear it."