From Sahih Bukhari (Hadith 5016):
Narrated `Aisha:Whenever Allah's Messenger (ﷺ) became sick, he would recite Mu'awwidhat (Surat Al-Falaq and Surat An- Nas) and then blow his breath over his body. When he became seriously ill, I used to recite (these two Suras) and rub his hands over his body hoping for its blessings
Reference: Bukhari 5016