Sahih Muslim 12620
In-book no 5343حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا نُوحُ بْنُ قَيْسٍ، عَنْ أَخِيهِ، خَالِدِ بْنِ قَيْسٍ عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم أَرَادَ أَنْ يَكْتُبَ إِلَى كِسْرَى وَقَيْصَرَ وَالنَّجَاشِيِّ . فَقِيلَ إِنَّهُمْ لاَ يَقْبَلُونَ كِتَابًا إِلاَّ بِخَاتِمٍ . فَصَاغَ رَسُولُ اللَّهِ صلى الله عليه وسلم خَاتَمًا حَلَقَةً فِضَّةً وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ .
Anas reported that when Allah's Apostle (ﷺ) decided to write to the Kisra (the King of Persia), Caesar (Emperor of Rome), and the Negus (the Emperor of Abyssinia), it was said to him that they would not accept the letter without the seal over it; so Allah's Messenger (ﷺ) got a seal made, the ring of which was made of silver and there was engraved on it: "Muhammad, the Messenger of Allah."