Sahih Bukhari Volume 8, Book 78, Hadith Number 646.

Narated By Ibn ‘Umar : Allah’s Apostle had a gold ring made for himself, and he used to wear it with the stone towards the inner part of his hand. Consequently, the people had similar rings made for themselves. Afterwards the Prophet; sat on the pulpit and took it off, saying, “I used to wear this ring and keep its stone towards the palm of my hand.” He then threw it away and said, “By Allah, I will never wear it.” Therefore all the people threw away their rings as well.