Musnad Ahmad 42
It was narrated that Rafi' atTaʼi, Abu Bakrʼs companion during the campaign of as-Salasil, said:
I asked him about how they came to swear allegiance to Abu Bakr and he said - when telling him about what the Ansar said and what Abu Bakr said to them and what `Umar bin al-Khattab said to the Ansar when he reminded them that he had led them in prayer on the instructions of the Messenger of Allah (ﷺ) when he was sick. They swore allegiance to me because of that and I Accepted it from them, but I was concerned that there would be turmoil that would lead to apostasy,
حَدَّثَنَا عَلِيُّ بْنُ عَيَّاشٍ، حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ، قَالَ أَخْبَرَنِي يَزِيدُ بْنُ سَعِيدِ بْنِ ذِي، عَصْوَانَ الْعَنْسِيُّ عَنْ عَبْدِ الْمَلِكِ بْنِ عُمَيْرٍ اللَّخْمِيِّ، عَنْ رَافِعٍ الطَّائِيِّ، رَفِيقِ أَبِي بَكْرٍ فِي غَزْوَةِ السُّلَاسِلِ قَالَ وَسَأَلْتُهُ عَمَّا قِيلَ مِنْ بَيْعَتِهِمْ فَقَالَ وَهُوَ يُحَدِّثُهُ عَمَّا تَكَلَّمَتْ بِهِ الْأَنْصَارُ وَمَا كَلَّمَهُمْ بِهِ وَمَا كَلَّمَ بِهِ عُمَرُ بْنُ الْخَطَّابِ الْأَنْصَارَ وَمَا ذَكَّرَهُمْ بِهِ مِنْ إِمَامَتِي إِيَّاهُمْ بِأَمْرِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي مَرَضِهِ فَبَايَعُونِي لِذَلِكَ وَقَبِلْتُهَا مِنْهُمْ وَتَخَوَّفْتُ أَنْ تَكُونَ فِتْنَةٌ تَكُونُ بَعْدَهَا رِدَّةٌ‏.‏