Musnad Ahmad 1156:93

Yahya ibn Ishaq narrated to us, he said: Layth ibn Sa’d narrated to me, Abdullah ibn Abi Mulaykah narrated to us, from Ya’la ibn Mamlak, he said: I asked Umm Salamah about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him, at night and his recitation. She said: "What do you have to do with his prayer and his recitation? He used to pray as much as he slept, and he used to sleep as much as he prayed." And she was describing his recitation, and it was a recitation that was clarified letter by letter. *** Abdullah ibn Muhammad narrated to us, [Abdullah ibn Ahmad said:] And I heard it myself from Abdullah ibn Muhammad ibn Abi Shaybah, he said: Jarir ibn Abd al-Hamid narrated to us, from Mughirah, from Umm Musa, from Umm Salamah, she said: "By the One by whom I swear, Ali was the closest of people in covenant to the Messenger of Allah, peace and blessings of Allah be upon him." She said: The Messenger of Allah, peace and blessings of Allah be upon him, visited us morning after morning, saying: "Has Ali come?" repeatedly. She said: And I think he had sent him on an errand. She said: Then he came, and I thought that he had a need for him, so we went out of the house and sat by the door. I was the closest of them to the door. Ali leaned over him, and he began to whisper to him and converse privately with him. Then the Messenger of Allah, peace and blessings of Allah be upon him, passed away on that very day, so he was the closest of people to him in covenant.