Musnad Abu Ya'la al-Mawsili 110:157

Abu Bakr ibn Abi Shaybah narrated to us, Abd al-Rahim ibn Sulayman narrated to us, from al-Hajjaj, from al-Minhal, from Abdullah ibn al-Harith, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever visits a sick person whose time of death has not yet arrived, and says seven times: 'I ask Allah the Magnificent, Lord of the Magnificent Throne, to heal you,' he will be healed."