Musannaf Ibn Abi Shayba 21:371

Abu al-Ahwas narrated to us, from Abu Ishaq, from al-Harith, from Ali, who said: When the Messenger of Allah (peace be upon him) would enter upon a sick person, he would say: "Remove the hardship, O Lord of the people, and heal, for You are the Healer. There is no healer except You."