Anas bin Malik reported,

When the Prophet ﷺ wanted to write to the Romans, he was told that they would not read any letter unless it was sealed. So he had a silver ring made, and it is as if I can still see its whiteness on his hand. Engraved on it was, "Muhammad, Messenger of Allah."

Bukhari 2938

Sahih

حدثنا علي بن الجعد أخبرنا شعبة عن قتادة قال سمعت

أنسا رضي الله عنه يقول

لما أراد النبي ﷺ أن يكتب إلى الروم قيل له إنهم لا يقرءون كتابا إلا أن يكون مختوما فاتخذ خاتما من فضة فكأني أنظر إلى بياضه في يده ونقش فيه محمد رسول الله

البخاري 2938صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Jihad and expeditions
Chapter
Inviting Jews and Christians to Islam, what they are fought over, and what the Prophet ﷺ wrote to Kisra and Qaysar
Numbering
Darussalam 2938
Bukhari 2938