Sahih Bukhari Volume 7, Book 77, Hadith 5881

قَالَ اَبُو عَبْدِاللهِ: وَزَادَنِي أَحْمَدُ: حَدَّثَنَا الأَنْصَارِيُّ، قَالَ حَدَّثَنِي أَبِي، عَنْ ثُمَامَةَ، عَنْ أَنَسٍ، قَالَ كَانَ خَاتَمُ النَّبِيِّ صلى الله عليه وسلم فِي يَدِهِ، وَفِي يَدِ أَبِي بَكْرٍ بَعْدَهُ، وَفِي يَدِ عُمَرَ بَعْدَ أَبِي بَكْرٍ، فَلَمَّا كَانَ عُثْمَانُ جَلَسَ عَلَى بِئْرِ أَرِيسَ ـ قَالَ ـ فَأَخْرَجَ الْخَاتَمَ، فَجَعَلَ يَعْبَثُ بِهِ فَسَقَطَ قَالَ فَاخْتَلَفْنَا ثَلاَثَةَ أَيَّامٍ مَعَ عُثْمَانَ فَنَنْزَحُ الْبِئْرَ فَلَمْ نَجِدْهُ‏.‏

Anas added: 'the ring of the Prophet was in his hand, and after him, in Abu Bakr's hand, and then in 'Umar's hand after Abu Bakr. When Uthman was the Caliph, once he was sitting at the well of Aris. He removed the ring from his hand and while he was trifling with it, dropped into the well. We kept on going to the well with Uthman for three days looking for the ring, and finally the well was drained, but the ring was not found.