Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that the Prophet of Allah (peace and blessings be upon him) said: "There is no man who visits a sick person and says seven times: 'I ask Allah the Mighty, Lord of the Mighty Throne, to cure you' while his time of death is still delayed, except that (his suffering) is surely eased."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12225