Musnad Ahmad 1153:814

Ibrahim ibn Abi al-Abbas narrated to us, he said: Abu Uways narrated to us, from al-Zuhri, that Urwah ibn al-Zubayr informed him that Aisha informed him: "That the Messenger of Allah, peace and blessings of Allah be upon him, when he was ill, would recite the Mu'awwidhat (the chapters of seeking refuge) over himself and blow (with a light spittle)." She said: Aisha said: "Then when the pain of the Messenger of Allah, peace and blessings of Allah be upon him, became severe, I would recite over him and wipe him with his own hand, hoping for its blessing."