أَخْبَرَنَا حُمَيْدُ بْنُ مَسْعَدَةَ، عَنْ بِشْرٍ، - وَهُوَ ابْنُ الْمُفَضَّلِ - قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ أَرَادَ رَسُولُ اللَّهِ صلى الله عليه وسلم أَنْ يَكْتُبَ إِلَى الرُّومِ فَقَالُوا إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ مَخْتُومًا . فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ كَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ وَنُقِشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ .
It was narrated that Anas said: "The Messenger of Allah [SAW] wanted to write to the Romans, and they (the Companions) said: 'They do not read any letter unless it has a seal.' So he took a ring of silver and it is as if I can see its whiteness on his hand, and engraved on it (were the words): 'Muhammad Rasul Allah.'" Translation Not Available
Book Ref: Sunan An Nisai Book 48 Hadith 5278
Web Ref: Sunan An Nisai Vol 6 Book 48 Hadith 5280