(21) باب اسْتِخْلاَفِ الإِمَامِ إِذَا عَرَضَ لَهُ عُذْرٌ مِنْ مَرَضٍ وَسَفَرٍ وَغَيْرِهِمَا مَنْ يُصَلِّي بِالنَّاسِ وَأَنَّ مَنْ صَلَّى خَلْفَ إِمَامٍ جَالِسٍ لِعَجْزِهِ عَنِ الْقِيَامِ لَزِمَهُ الْقِيَامُ إِذَا قَدَرَ عَلَيْهِ وَنَسْخِ الْقُعُودِ خَلْفَ الْقَاعِدِ فِي حَقِّ مَنْ قَدَرَ عَلَى الْقِيَامِ
'A'isha, the wife of the Apostle (ﷺ), said:
When the Messenger of Allah (ﷺ) fell ill and his illness became serious, he asked permission from his wives to stay in my house during his illness. They gave him permission to do so. He stepped out (of'A'isha's apartment for prayer) supported by two persons. (He was so much weak) that his feet dragged on the ground and he was being supported by 'Abbas b. 'Abd al-Muttalib and another person. 'Ubaidullah said: I informed 'Abdullah (b. 'Abbas) about that which 'A'isha had said. 'Abdullah b. 'Abbas said: Do you know the man whose name 'A'isha did not mention? He said: No. Ibn 'Abbas said: It was 'Ali.
Reference: Sahih Muslim 418 c
In-book reference: Book 4, Hadith 100
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 834