Any Muslim servant who visits a sick person whose prescribed moment of death has not arrived and supplicates seven times:
أَسْأَلُ اللَّهَ الْعَظِيمَ رَبَّ الْعَرْشِ الْعَظِيمِ أَنْ يَشْفِيَكَ
I ask Almighty Allah, Lord of the Magnificent Throne, to make you well.
As'alullaahal-'Adheema Rabbal-'Arshil-'Adheemi 'an yashfiyaka.
At-Tirmithi, Abu Dawud. See also Al-Albani, Sahih At-Tirmithi 2/210 and Sahihul-Jami' As-Saghir 5/180.