أَخْبَرَنَا عِمْرَانُ بْنُ مُوسَى، قَالَ حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنْ عَبْدِ الْعَزِيزِ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم اصْطَنَعَ خَاتَمًا فَقَالَ ‏"‏ إِنَّا قَدِ اتَّخَذْنَا خَاتَمًا وَنَقَشْنَا عَلَيْهِ نَقْشًا فَلاَ يَنْقُشْ عَلَيْهِ أَحَدٌ ‏"‏ ‏.‏ وَإِنِّي لأَرَى بَرِيقَهُ فِي خِنْصَرِ رَسُولِ اللَّهِ صلى الله عليه وسلم ‏.‏

It was narrated from Anas that: The Prophet [SAW] had a ring and he said: "We have had a ring made with an inscription, and no one else should copy this inscription." It is as if I can see its shining on the little finer of the Messenger of Allah [SAW]. Translation Not Available

Book Ref: Sunan An Nisai Book 48 Hadith 5282
Web Ref:  Sunan An Nisai Vol 6 Book 48 Hadith 5284