Sahih Muslim Book 024, Hadith Number 5210.
Chapter : About the signet ring made of gold.
'Abdullah reported that Allah's Messenger (may peace be upon him) got fashioned a signet ring of gold but he kept its stone on the inner side of his palm as he wore it, so the people (following his example) got fashioned (such rings). Then one day as he sat on the pulpit he pulled it away saying: I wore this ring and kept its stone towards the inner side. He then threw it away, and said: By Allah, I will never wear it; so the people threw their rings away.