Anas said that when the Prophet wanted to write to the Persian Emperor, the Byzantine Emperor and the Negus he was told that they would not accept a letter without a seal; so God’s messenger fashioned a seal in the form of a silver ring on which he engraved “Muhammad God’s messenger.” Muslim transmitted it. A version by Bukhari says the engraving on the seal was in three lines, “Muhammad” being one, “messenger” another, and “of God” another.
Hadith Referenceمشكوة المصابيح / كتاب اللباس / 4386
Hadith Gradingالألبانی:صَحِيح | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (5875، 5878) و مسلم (2092/58)»