Musnad Ahmad 27:692

'Abd al-Rahman ibn Mahdi narrated to us, Za'idah narrated to us, from Musa ibn Abi 'Aishah, from 'Ubayd Allah ibn 'Abd Allah, who said: I entered upon 'Aishah and said: "Will you not tell me about the illness of the Messenger of Allah (ﷺ)?" She said: "Yes. The Messenger of Allah (ﷺ) became very ill and said: 'Have the people prayed?' We said: 'No, they are waiting for you, O Messenger of Allah.' He said: 'Put water for me in the washbasin.' We did so, and he performed ghusl. Then he went to stand up, but he fainted. Then he regained consciousness and said: 'Have the people prayed?' We said: 'No, they are waiting for you, O Messenger of Allah.' He said: 'Put water for me in the washbasin.' We did so, and he performed ghusl. Then he went to stand up, but he fainted. Then he regained consciousness and said: 'Have the people prayed?' We said: 'No, they are waiting for you, O Messenger of Allah.' He said: 'Put water for me in the washbasin.' He went to stand up, but he fainted." She said: "The people were staying in the mosque, waiting for the Messenger of Allah (ﷺ) for the night prayer (Isha). The Messenger of Allah (ﷺ) sent word to Abu Bakr to lead the people in prayer. Abu Bakr was a tender-hearted man, so he said: 'O 'Umar, lead the people in prayer.' 'Umar said: 'You are more entitled to that.' So Abu Bakr led them in prayer during those days." "Then the Messenger of Allah (ﷺ) felt some relief, so he went out between two men, one of whom was al-'Abbas, for the noon prayer (Dhuhr). When Abu Bakr saw him, he went to step back, but he (the Prophet) gestured to him not to step back. He ordered them, so they seated him beside him. Abu Bakr began to pray standing, while the Messenger of Allah (ﷺ) prayed sitting." I entered upon Ibn 'Abbas and said: "Shall I present to you what 'Aishah told me regarding the illness of the Messenger of Allah (ﷺ)?" He said: "Bring it forth." So I told him, and he did not deny any of it, except that he said: "Did she name to you the man who was with al-'Abbas?" I said: "No." He said: "He was 'Ali, may Allah have mercy upon him."