Musnad Ahmad 25:217

Yahya ibn Zakariya ibn Abi Za'idah narrated to us, my father narrated to me, from Abu Ishaq, from al-Arqam ibn Sharhabil, from Ibn Abbas, who said: "When the Prophet, peace and blessings of Allah be upon him, became ill, he ordered Abu Bakr to lead the people in prayer. Then he felt a lightness, so he went out. When Abu Bakr sensed him, he wanted to retreat, but the Prophet, peace and blessings of Allah be upon him, gestured to him. So he sat beside Abu Bakr on his left, and he began the recitation from the verse where Abu Bakr had reached."