(5) باب مَا ذُكِرَ مِنْ دِرْعِ النَّبِيِّ صلى الله عليه وسلم وَعَصَاهُ وَسَيْفِهِ وَقَدَحِهِ وَخَاتَمِهِ
Narrated Anas:
That when Abu Bakr became the Caliph, he sent him to Bahrain and wrote this letter for him, and stamped it with the Ring of the Prophet. Three lines were engraved on the Ring, (the word) 'Muhammad' was in a line, 'Apostle' was in another line, and 'Allah' in a third.
Reference: Sahih al-Bukhari 3106
In-book reference: Book 57, Hadith 15
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 53, Hadith 338