Chapter: To bear witness as to the writer of a stamped letter; and the letter of a ruler to a governor, and of a judge to a judge
Narrated Anas bin Malik:When the Prophet (ﷺ) intended to write to the Byzantines, the people said, "They do not read a letter unless it is sealed (stamped)." Therefore the Prophet (ﷺ) took a silver ring----as if I am looking at its glitter now----and its engraving was: 'Muhammad, Apostle of Allah'.
Reference
Sahih al-Bukhari 7162
In-book reference
Book 93, Hadith 26
USC-MSA web (English)
Vol. 9, Book 89, Hadith 276
Translation by Dr. M. Muhsin Khan · Language: EN
Sahih
Arabic Text
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، قَالَ سَمِعْتُ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ لَمَّا أَرَادَ النَّبِيُّ صلى الله عليه وسلم أَنْ يَكْتُبَ إِلَى الرُّومِ قَالُوا إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ مَخْتُومًا. فَاتَّخَذَ النَّبِيُّ صلى الله عليه وسلم خَاتَمًا مِنْ فِضَّةٍ، كَأَنِّي أَنْظُرُ إِلَى وَبِيصِهِ، وَنَقْشُهُ مُحَمَّدٌ رَسُولُ اللَّهِ.