Musannaf Ibn Abi Shayba 21:374

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