Musnad Ahmad 27:1547

Hashim narrated to us, Layth narrated to us, Nafi’ narrated from Abdullah, that the Messenger of Allah (peace and blessings of Allah be upon him) had a ring of gold made, and he used to place its stone on the inside of his palm when he wore it, so the people did the same. Then he sat upon the pulpit and removed it, and said: "I used to wear this ring and place its stone on the inside." Then he threw it away and said: "By Allah, I will never wear it again." So the people threw away their rings.