When Abu Bakr was appointed caliph, he sent him to Bahrain and wrote this letter for him, sealing it with the ring. The engraving on the ring consisted of three lines, Muhammad on one line, Messenger on another, and Allah on the third.
أن أبا بكر لما استخلف بعثه إلى البحرين، وكتب له هذا الكتاب وختمه، وكان نقش الخاتم ثلاثة أسطر محمد سطر، ورسول سطر والله سطر.
Bukhari narrated it in the Book of the Obligation of Khumus (3106) and in the Book of Dress (5878) from Muhammad bin Abdullah Ansari, who said, my father narrated to me, from Thumamah, from Anas, who said, and then he mentioned it.