Sunan an-Nasa'i 834
It was narrated that 'Ubaidullah bin 'Abdullah said:
"I entered upon Aisha and said: 'Will you not tell me about the sickness of the Messenger of Allah (ﷺ)?' She said: 'When the Messenger of Allah (ﷺ), became seriously ill, he said: "Have the people prayed?" We said: "No, they are waiting for you, 0 Messenger of Allah (ﷺ)" He said: "Put some water in a tub for me." We did that and he performed Ghusl, then he tried to  get up but he fainted. Then he came to us and said: "Have the people prayed?" We said: "No, they are waiting for you, 0 Messenger of
Allah (ﷺ)." He said: "Put some water in
a tub for me." We did that and he performed Ghusl, then he tried to get up but he fainted. Then for the third time he said the same thing. She said: The people were in the Masjid, waiting for the Messenger of Allah (ﷺ) to lead the prayer. The Messenger of Allah (ﷺ) sent word to Abu Bakr, telling him to lead the people in prayer, so the messenger came to him and said: "The Messenger of Allah (ﷺ) is telling you  to lead the people in prayer." Abu Bakr was a tenderhearted man, he said: "0 'Umar. lead the 
in prayer." But ('Umar) said: "You have more right to that." So Abu Bakr led them in prayer during those days. When the Messenger of Allah (ﷺ) felt a little better, he came with
the help of two men, one of whom was Al-'Abbas, to pray Zuhr. When Abu Bakr saw him, he wanted to step back, but the Messenger of Allah (ﷺ) gestured to him not to step back. He told them (the two men) to seat him beside Abu Bakr, and Abu Bakr started to pray standing. The people were following the prayer of Abu Bakr and the Messenger of Allah (ﷺ) was praying sitting."'
"I ('Ubaidullah) entered upon Ibn Abbas and said 'Shall I not tell you what Aisha narrated to me about the sickness of the Messenger of Allah (ﷺ)?' He said: 'Yes.' So I told him and he did not deny any of it, but he said: 'Did she tell you the name of the man who was with Al-'Abbas?' I said: 'No.' He said: 'That
was Ali, may Allah honor his face."'
أَخْبَرَنَا الْعَبَّاسُ بْنُ عَبْدِ الْعَظِيمِ الْعَنْبَرِيُّ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، قَالَ حَدَّثَنَا زَائِدَةُ، عَنْ مُوسَى بْنِ أَبِي عَائِشَةَ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، قَالَ دَخَلْتُ عَلَى عَائِشَةَ فَقُلْتُ أَلاَ تُحَدِّثِينِي عَنْ مَرَضِ رَسُولِ اللَّهِ صلى الله عليه وسلم ‏.‏ قَالَتْ لَمَّا ثَقُلَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏"‏ أَصَلَّى النَّاسُ ‏"‏ ‏.‏ فَقُلْنَا لاَ وَهُمْ يَنْتَظِرُونَكَ يَا رَسُولَ اللَّهِ ‏.‏ فَقَالَ ‏"‏ ضَعُوا لِي مَاءً فِي الْمِخْضَبِ ‏"‏ ‏.‏ فَفَعَلْنَا فَاغْتَسَلَ ثُمَّ ذَهَبَ لِيَنُوءَ فَأُغْمِيَ عَلَيْهِ ثُمَّ أَفَاقَ فَقَالَ ‏"‏ أَصَلَّى النَّاسُ ‏"‏ ‏.‏ قُلْنَا لاَ هُمْ يَنْتَظِرُونَكَ يَا رَسُولَ اللَّهِ ‏.‏ فَقَالَ ‏"‏ ضَعُوا لِي مَاءً فِي الْمِخْضَبِ ‏"‏ ‏.‏ فَفَعَلْنَا فَاغْتَسَلَ ثُمَّ ذَهَبَ لِيَنُوءَ ثُمَّ أُغْمِيَ عَلَيْهِ ثُمَّ قَالَ فِي الثَّالِثَةِ مِثْلَ قَوْلِهِ قَالَتْ وَالنَّاسُ عُكُوفٌ فِي الْمَسْجِدِ يَنْتَظِرُونَ رَسُولَ اللَّهِ صلى الله عليه وسلم لِصَلاَةِ الْعِشَاءِ فَأَرْسَلَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى أَبِي بَكْرٍ ‏"‏ أَنْ صَلِّ بِالنَّاسِ ‏"‏ ‏.‏ فَجَاءَهُ الرَّسُولُ فَقَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم يَأْمُرُكَ أَنْ تُصَلِّيَ بِالنَّاسِ وَكَانَ أَبُو بَكْرٍ رَجُلاً رَقِيقًا فَقَالَ يَا عُمَرُ صَلِّ بِالنَّاسِ ‏.‏ فَقَالَ أَنْتَ أَحَقُّ بِذَلِكَ ‏.‏ فَصَلَّى بِهِمْ أَبُو بَكْرٍ تِلْكَ الأَيَّامَ ثُمَّ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم وَجَدَ مِنْ نَفْسِهِ خِفَّةً فَجَاءَ يُهَادَى بَيْنَ رَجُلَيْنِ أَحَدُهُمَا الْعَبَّاسُ لِصَلاَةِ الظُّهْرِ فَلَمَّا رَآهُ أَبُو بَكْرٍ ذَهَبَ لِيَتَأَخَّرَ فَأَوْمَأَ إِلَيْهِ رَسُولُ اللَّهِ صلى الله عليه وسلم أَنْ لاَ يَتَأَخَّرَ وَأَمَرَهُمَا فَأَجْلَسَاهُ إِلَى جَنْبِهِ فَجَعَلَ أَبُو بَكْرٍ يُصَلِّي قَائِمًا وَالنَّاسُ يُصَلُّونَ بِصَلاَةِ أَبِي بَكْرٍ وَرَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي قَاعِدًا ‏.‏ فَدَخَلْتُ عَلَى ابْنِ عَبَّاسٍ فَقُلْتُ أَلاَ أَعْرِضُ عَلَيْكَ مَا حَدَّثَتْنِي عَائِشَةُ عَنْ مَرَضِ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ نَعَمْ ‏.‏ فَحَدَّثْتُهُ فَمَا أَنْكَرَ مِنْهُ شَيْئًا غَيْرَ أَنَّهُ قَالَ أَسَمَّتْ لَكَ الرَّجُلَ الَّذِي كَانَ مَعَ الْعَبَّاسِ قُلْتُ لاَ ‏.‏ قَالَ هُوَ عَلِيٌّ كَرَّمَ اللَّهُ وَجْهَهُ ‏.‏