When Abu Bakr was appointed caliph, it was written for him that the inscription on the seal consisted of three lines, Muhammad on one line, Messenger on another, and Allah on another.
أن أبا بكر لما استخلف كتب له، وكان نقش الخاتم ثلاثة أسطر: محمد سطر، ورسول سطر، والله سطر.
Bukhari narrated it in the Book of Dress (5878) from Muhammad bin Abdullah Ansari, who said, my father narrated to me, from Thumama, from Anas, and he mentioned it. Bukhari said, Ahmad added for me, Ansari narrated to us, he said, my father narrated to me, from Thumama, from Anas, who said, "The ring of the Prophet ﷺ was on his hand, and then on the hand of Abu Bakr after him, and on the hand of Umar after Abu Bakr. When Uthman's turn came, he sat by the well of Aris." He said, "He took out the ring and began playing with it, and it fell in." He said, "So we searched for three days with Uthman, and we drained the well, but we did not find it."As for his statement "Ahmad added for me," he means Ahmad bin Hanbal, as Mizzi confirmed decisively in al-Atraf, except that Imam Ahmad did not mention this story in his Musnad, so it is possible that this Ahmad is someone other than Ibn Hanbal.As for his statement "he wrote for him," it means that when Abu Bakr became caliph, he sent Anas bin Malik to Bahrain and wrote this letter for him and sealed it, and the engraving on the ring consisted of three lines. Bukhari narrated it in the Book of Obligation of Khumus (3106).