(13) باب فِي اتِّخَاذِ النَّبِيِّ صلى الله عليه وسلم خَاتَمًا لَمَّا أَرَادَ أَنْ يَكْتُبَ إِلَى الْعَجَمِ
Anas reported that when Allah's Apostle (ﷺ) decided to write (letters) to non-Arabs (i. e. Persian and Byzantine Emperors) it was said to him that the non-Arabs would not accept a letter but that having a seal over it; so he (the Holy Prophet) got a silver ring made. He (Anas) said:
I perceive as if I am looking at its brightness in his hand.
Reference: Sahih Muslim 2092 d
In-book reference: Book 37, Hadith 96
USC-MSA web (English) reference(deprecated numbering scheme): Book 24, Hadith 5217