Sunan an-Nasa'i, Book 48, Hadith 161 (In-Book) ⓘ
It was narrated that Anas said: "The ring of the Prophet [SAW] was made of silver and its stone (Fass) was made of silver too."
أَخْبَرَنَا أَحْمَدُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنَا مُوسَى بْنُ دَاوُدَ، قَالَ حَدَّثَنَا زُهَيْرُ بْنُ مُعَاوِيَةَ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ كَانَ خَاتَمُ النَّبِيِّ صلى الله عليه وسلم مِنْ فِضَّةٍ فَصُّهُ مِنْهُ .
also referenced under: Hadith 5200 (Reference) & Volume 6, Book 48, Hadith 5203 (DarusSalam)