Musnad Ahmad 27:1512

Al-Fadl narrated to us, Sufyan narrated to us, from Abdullah ibn Dinar, who said: I heard Ibn Umar saying: The Messenger of Allah (peace and blessings of Allah be upon him) took a ring of gold, so the people took rings of gold. Then the Messenger of Allah (peace and blessings of Allah be upon him) said: "I had taken a ring of gold, but I have cast it away." And he said: "I will never wear it." So the people cast away their rings.