When the Prophet of Allah ﷺ intended to write to the non-Arabs, he was told that they would not accept any letter unless it bore a seal. So he had a seal made. The narrator said, "It is as if I can still see its whiteness on his palm."
حدثنا إسحق بن منصور أخبرنا معاذ بن هشام حدثني أبي عن قتادة
لما أراد نبي الله ﷺ أن يكتب إلى العجم قيل له إن العجم لا يقبلون إلا كتابا عليه خاتم فاصطنع خاتما قال فكأني أنظر إلى بياضه في كفه
Muslim also narrated it in "The Book of Clothing and Adornment," chapter on the Prophet's ﷺ adoption of a signet ring when he wanted to write to the non-Arabs, hadith no. 57/2092, from the hadith of Muaz bin Hisham with the same wording. Bukhari also narrated it, hadith no. 65, from the hadith of Qatada with the same wording.