Sahih Bukhari Volume 6, Book 66, Hadith 5018

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، رضى الله عنها أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا اشْتَكَى يَقْرَأُ عَلَى نَفْسِهِ بِالْمُعَوِّذَاتِ وَيَنْفُثُ، فَلَمَّا اشْتَدَّ وَجَعُهُ كُنْتُ أَقْرَأُ عَلَيْهِ وَأَمْسَحُ بِيَدِهِ رَجَاءَ بَرَكَتِهَا‏

Narrated By 'Aisha : Whenever Allah's Apostle 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.