Musnad Ahmad 27:1811

Ibn Numayr narrated to us, Ubayd Allah narrated to us, from Nafi’, from Ibn Umar, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) took a ring of silver, and it was in his hand. Then it was in the hand of Abu Bakr after him, then it was in the hand of Umar, then it was in the hand of Uthman. Its inscription was 'Muhammad the Messenger of Allah'."