Sahih Muslim Book - 37, Hadith - 5481

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ ، حَدَّثَنِي أَبِي ، عَنْ قَتَادَةَ ، عَنْ أَنَسٍ ، أَنَّ نَبِيَّ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ أَرَادَ أَنْ يَكْتُبَ إِلَى الْعَجَمِ ، فَقِيلَ لَهُ: إِنَّ الْعَجَمَ لاَ يَقْبَلُونَ إِلاَّ كِتَابًا عَلَيْهِ خَاتَمٌ ، فَاصْطَنَعَ خَاتَمًا مِنْ فِضَّةٍ. قَالَ:كَأَنِّي أَنْظُرُ إِلَى بَيَاضِهِ فِي يَدِهِ.

It was narrated from Anas that the Prophet of Allah (s.a.w) wanted to send a letter to the non-Arabs, and it was said to him: "The non-Arabs do not read any letter unless it has a seal on it." So he had a ring of silver made. He said: "It is as if I can see its brightness on his hand."