Sunan an-Nasa'i, Book 48, Hadith 249 (In-Book) ⓘ

It was narrated that Ibn 'Umar said: "The Prophet [SAW] wore a ring of gold, then he discarded it and wore a ring of silver on which were engraved (the words) 'Muhammad Rasul Allah.' Then he said: 'No one should copy this inscription of mine.' And he wore the stone (Fass) toward his palm."

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ يَزِيدَ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ أَيُّوبَ بْنِ مُوسَى، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يَتَخَتَّمُ بِخَاتَمٍ مِنْ ذَهَبٍ ثُمَّ طَرَحَهُ وَلَبِسَ خَاتَمًا مِنْ وَرِقٍ وَنُقِشَ عَلَيْهِ مُحَمَّدٌ رَسُولُ اللَّهِ ثُمَّ قَالَ ‏ "‏ لاَ يَنْبَغِي لأَحَدٍ أَنْ يَنْقُشَ عَلَى نَقْشِ خَاتَمِي هَذَا ‏" ‏ ‏.‏ وَجَعَلَ فَصَّهُ فِي بَطْنِ كَفِّهِ ‏.‏