The Messenger of Allah ﷺ wanted to write to some persian rulers. He was told that they would not read a letter without a seal in the form of a silver ring on which he engraved "Muhammad the Messenger of Allah."  

أَرَادَ رَسُولُ اللَّهِ ﷺ أَنْ يَكْتُبَ إِلَى بَعْضِ الأَعَاجِمِ فَقِيلَ لَهُ إِنَّهُمْ لاَ يَقْرَءُونَ كِتَابًا إِلاَّ بِخَاتَمٍ فَاتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ  

It remained in his hand until he died, in the hand of 'Abu Bakr until he died, in the hand of 'Umar until he died, and in the hand of 'Uthman. When he was near a well, it fell down in it. He ordered to take it out, but it could not be found.  

عَنْ أَنَسٍ بِمَعْنَى حَدِيثِ عِيسَى بْنِ يُونُسَ زَادَ فَكَانَ فِي يَدِهِ حَتَّى قُبِضَ وَفِي يَدِ أَبِي بَكْرٍ حَتَّى قُبِضَ وَفِي يَدِ عُمَرَ حَتَّى قُبِضَ وَفِي يَدِ عُثْمَانَ فَبَيْنَمَا هُوَ عِنْدَ بِئْرٍ إِذْ سَقَطَ فِي الْبِئْرِ فَأَمَرَ بِهَا فَنُزِحَتْ فَلَمْ يُقْدَرْ عَلَيْهِ  

The signet-ring of the Prophet ﷺ was of silver with an Abyssinian stone.  

كَانَ خَاتَمُ النَّبِيِّ ﷺ مِنْ وَرِقٍ فَصُّهُ حَبَشِيٌّ  

The signet-ring of the Prophet ﷺ was all of silver as was also its stone.  

كَانَ خَاتَمُ النَّبِيِّ ﷺ مِنْ فِضَّةٍ كُلُّهُ فَصُّهُ مِنْهُ  

The Messenger of Allah ﷺ took a signet-ring of gold, and put the stone next the palm of his hand. He engraved on it "Muhammad, the Messenger of Allah". The people then took signet-rings of gold. When he saw that they had taken them (like his ring) he threw it away and said: I shall never wear it. He then fashioned a silver ring and engraved on it "Muhammad, the Messenger of Allah". Then Abu Bakr wore it after him, then 'Umar wore it after Abu Bakr, and the 'Uthman wore it after 'Umar till it fell down in a well called Aris. Abu Dawud said: The people did not disagree on 'Uthman till the signet-rin fell down from his hand.  

اتَّخَذَ رَسُولُ اللَّهِ ﷺ خَاتَمًا مِنْ ذَهَبٍ وَجَعَلَ فَصَّهُ مِمَّا يَلِي بَطْنَ كَفِّهِ وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ فَاتَّخَذَ النَّاسُ خَوَاتِمَ الذَّهَبِ فَلَمَّا رَآهُمْ قَدِ اتَّخَذُوهَا رَمَى بِهِ وَقَالَ لاَ أَلْبَسُهُ أَبَدًا ثُمَّ اتَّخَذَ خَاتَمًا مِنْ فِضَّةٍ نَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ ثُمَّ لَبِسَ الْخَاتَمَ بَعْدَهُ أَبُو بَكْرٍ ثُمَّ لَبِسَهُ بَعْدَ أَبِي بَكْرٍ عُمَرُ ثُمَّ لَبِسَهُ بَعْدَهُ عُثْمَانُ حَتَّى وَقَعَ فِي بِئْرِ أَرِيسَ  

He engraved on it "Muhammad, the Messenger of Allah." and said: "No one must engrave anything in the manner of this signet-ring of mine. He then transmitted the rest of the tradition.  

عَنِ النَّبِيِّ ﷺ فَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ وَقَالَ لاَ يَنْقُشْ أَحَدٌ عَلَى نَقْشِ خَاتَمِي هَذَا ثُمَّ سَاقَ الْحَدِيثَ  

They searched for it but could not find it. 'Uthman then fashioned a signet-ring and engraved on it "Muhammad, the Messenger of Allah". He used to wear it or stamp with it.  

عَنِ النَّبِيِّ ﷺ قَالَ فَالْتَمَسُوهُ فَلَمْ يَجِدُوهُ فَاتَّخَذَ عُثْمَانُ خَاتَمًا وَنَقَشَ فِيهِ مُحَمَّدٌ رَسُولُ اللَّهِ قَالَ فَكَانَ يَخْتِمُ بِهِ أَوْ يَتَخَتَّمُ بِهِ