Language:
كتاب فرض الخمس
57  
One-fifth of Booty to the Cause of Allah (Khumus)
(5)
Chapter: What has been said regarding the armour of the Prophet ﷺ, his staff, sword, cup and ring, and what the caliphs after him used of these things which had not been distributed, and also (what is said) about his hair, shoes and utensils which were considered as blessed things by his companions and others after his death
(5)
باب مَا ذُكِرَ مِنْ دِرْعِ النَّبِيِّ صلى الله عليه وسلم وَعَصَاهُ وَسَيْفِهِ وَقَدَحِهِ وَخَاتَمِهِ وَمَا اسْتَعْمَلَ الْخُلَفَاءُ بَعْدَهُ مِنْ ذَلِكَ مِمَّا لَمْ يُذْكَرْ قِسْمَتُهُ، وَمِنْ شَعَرِهِ وَنَعْلِهِ وَآنِيَتِهِ، مِمَّا يَتَبَرَّكُ أَصْحَابُهُ وَغَيْرُهُمْ بَعْدَ وَفَاتِهِ
Sahih al-Bukhari 3106

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.

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الأَنْصَارِيُّ، قَالَ حَدَّثَنِي أَبِي، عَنْ ثُمَامَةَ، عَنْ أَنَسٍ، أَنَّ أَبَا بَكْرٍ ـ رضى الله عنه ـ لَمَّا اسْتُخْلِفَ بَعَثَهُ إِلَى الْبَحْرَيْنِ، وَكَتَبَ لَهُ هَذَا الْكِتَابَ وَخَتَمَهُ، وَكَانَ نَقْشُ الْخَاتَمِ ثَلاَثَةَ أَسْطُرٍ مُحَمَّدٌ سَطْرٌ، وَرَسُولُ سَطْرٌ، وَاللَّهِ سَطْرٌ‏.‏
Reference : Sahih al-Bukhari 3106
In-book reference : Book 57, Hadith 15
USC-MSA web (English) reference : Vol. 4, Book 53, Hadith 338
  (deprecated numbering scheme)