Anas bin Malik reported,
When Abu Bakr 
was appointed caliph, a seal was engraved for him. The inscription on the seal consisted of three lines, Muhammad on one line, Messenger on another, and Allah on the third.
Bukhari 5878
Difficultحدثني محمد بن عبد الله الأنصاري قال حدثني أبي عن ثمامة
عن أنس
أن أبا بكر رضي الله عنه لما استخلف كتب له وكان نقش الخاتم ثلاثة أسطر محمد سطر ورسول سطر والله سطر
البخاري 5878مشكل
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Clothing
Chapter
Should the engraving of the ring be made in three lines
Numbering
Darussalam 5878
Details
Collection
Sahih Bukhari
Book
Clothing
Chapter
Should the engraving of the ring be made in three lines
Numbering
Darussalam 5878
Ayat
No annotations are available.
Reference
Commentary
الدارقطني
It was also reported with this same chain, "The inscription on the seal was in three lines." The discussion of it is the same as the discussion of the first one.
Ibn Hajar
Hafiz said in Fath al-Bari, commenting on the report from Anas in the version of Ismaili, via Ali bin Madini, from Muhammad bin Abdullah Ansari, "My father narrated to me, Thumamah narrated to us, Anas narrated to me." End of quote.