Musnad Ahmad 32:2147

'Affan narrated to us, Hammam narrated to us, he said: 'Abd al-'Aziz ibn Suhayb informed us, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) took a ring and engraved an engraving upon it. He said: "I have taken a ring and engraved an engraving upon it, so let no one engrave upon its engraving."