Sunan an-Nasa'i, Volume 6, Book 48, Hadith 5199 (DarusSalam) ⓘ
It was narrated from Anas that : The Prophet [SAW] wore a ring of silver with an Ethiopian stone (Fass), on which was inscribed (the phrase): "Muhammad Rasul Allah (Muhammad the Messenger of Allah)."
أَخْبَرَنَا الْعَبَّاسُ بْنُ عَبْدِ الْعَظِيمِ الْعَنْبَرِيُّ، قَالَ حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، قَالَ حَدَّثَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم اتَّخَذَ خَاتَمًا مِنْ وَرِقٍ فَصُّهُ حَبَشِيٌّ وَنُقِشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ .
also referenced under: Hadith 5196 (Reference) & Book 48, Hadith 157 (In-Book)