Abdullah ibn Buraydah reported on the authority of his father that a man came to the Prophet He had an iron ring on his hand. He asked, “Why is it that I see on you the adornment of the people of Fire?” When he came again, he wore a ring of yellow copper, and the Prophet (SAW) said, ‘Why do I smell the odour of idols on you?” Then the next time he had on him a ring of gold, and he asked him, “Why is it that I see on you the ornament of the inhabitants of paradise?” He asked, “What material should I select?” He said, “Silver, but not weighing as much as a mithqal.’
[Abu Dawud 4223]
--------------------------------------------------------------------------------