Musnad Ahmad 27:1952

Safwan ibn Isa narrated to us, Usamah ibn Zayd informed us, from Nafi, from Abdullah, that the Prophet, peace and blessings of Allah be upon him, took a ring of gold and placed it on his right hand, and he placed its stone toward the inside of his palm. The people then took rings of gold. He said: So the Messenger of Allah, peace and blessings of Allah be upon him, ascended the pulpit and threw it away, and he forbade the wearing of gold rings.