(78) باب صِفَةِ خَاتَمِ النَّبِيِّ صلى الله عليه وسلم وَنَقْشِهِ
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.'"
Reference: Sunan an-Nasa'i 5278
In-book reference: Book 48, Hadith 239
English translation: Vol. 6, Book 48, Hadith 5280