Prophet Muhammad (P) when he visited the sick, used to comfort him and say the following Prayer for the Sick

"O Allah remove the hardship, O Lord of mankind, grant cure for You are the Healer. There is no cure but from You, a cure which leaves no illness behind."
Transliteration
- "Allahumma Azhibil bas, Rabbannas, Ishfi wa anta Shafi, La Shifa illa Shafaok. Shifaal La Yoghadiro saqama."