عَنْ أَنَسِ بْنِ مَالِكٍ رَضِيَ اللَّهُ عَنْهُ قَالَ لَمَّا أَرَادَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ أَنْ يَكْتُبَ إِلَى الرُّومِ قَالُوا إِنَّهُمْ لَا يَقْرَءُونَ كِتَابًا إِلَّا مَخْتُومًا قَالَ فَاتَّخَذَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ خَاتَمًا مِنْ فِضَّةٍ كَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ نَقْشُهُ مُحَمَّدٌ رَسُولُ اللَّهِ
Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that when the Noble Prophet (peace and blessings be upon him) intended to write a letter to the Romans, the people said to him that they only read a letter which has a seal on it. So the Noble Prophet (peace and blessings be upon him) had a silver ring made. It is as if I am still seeing the whiteness of that ring in the hand of the Noble Prophet (peace and blessings be upon him). The words "Muhammad Rasul Allah" were engraved on it.