Sahih Al Bukhari – Book of Medicine

Volumn 007, Book 071, Hadith Number 644. 
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Narated By 'Aisha RA : Whenever Allah's Apostle PBUH went to bed, he used to recite Surat-al-Ikhlas, Surat-al-Falaq and Surat-an-Nas and then blow on his palms and pass them over his face and those parts of his body that his hands could reach. And when he fell ill, he used to order me to do like that for him.