´Narrated Anas bin Malik:` "When the Prophet of Allah (ﷺ) wanted to write to the foreigners, it was said to him: 'The foreigners do not accept a letter unless it has a seal.' So he had a ring made." He said: "It is as if I am now looking at its whiteness in his hand."
Hadith Referenceسنن ترمذي / كتاب الاستئذان والآداب عن رسول الله صلى الله عليه وسلم / 2718