Mishkat al-Masabih 22 Clothing كتاب اللباس 78

وَعَنْهُ أَنَّ نَبِيَّ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ خَاتَمُهُ مِنْ فِضَّةٍ وَكَانَ فَصُّهُ مِنْهُ. رَوَاهُ البُخَارِيّ

He said the Prophet’s signet-ring was of silver as was also its stone. Bukhari transmitted it.