(7) CHAPTER. What is said regarding the hand to hand exchange (of books of knowledge), and the writing of knowledge by religious scholars to different countries.
Narrated Anas bin Malik: Once the Prophet wrote a letter or had an idea of writing a letter. The Prophet was told that they (rulers) would not read letters unless they were sealed. So the Prophet got a silver ring made with Muhammad Allah's Apostle engraved on it. As if I were just observing its white glitter in the hand of the Prophet.
Authentic