(Seven times)

أَسْأَلُ اللَّهَ الْعَظِيْمَ رَبَّ الْعَرْشِ الْعَظِيْمِ أَنْ يَشْفِيَكَ

As'alullaahal-'Adheem Rabbal-'Arshil-'Adheem 'an yashfiyak

I ask Almighty Allah, Lord of the Magnificent Throne, to make you well. Ibn 'Abbas (RA) narrated that the Prophet (ﷺ) said: "There is no Muslim worshiper who visits one who is ill - other than at the time of death - and he says seven times: (The dua is mentioned above) except when he will be cured." (The dua is mentioned above)

Reference: Sahih. Tirmidhi: 2083