Sahih Bukhari
Dress
Volume: 007 / Book Number: 072 / Hadith Number: 761
Narrated Anas bin Malik:
Allah's Apostle wanted to write a letter to a group of people or some non-Arabs. It was said to him, "They do not accept any letter unless it is stamped." So the Prophet had a silver ring made for himself, and on it was engraved: 'Muhammad, the Apostle of Allah'. .. as if I am now looking at the glitter of the ring on the finger (or in the palm) of the Prophet .