Sahih Bukhari Volume 004, Book 053, Hadith Number 338.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 53. One-Fifth Of Booty to the Cause Of Allah (Khumus)
Narated By 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.