The Prophet, during his fatal ailment used to blow (on his hands and pass them) over his body while reciting the Mu'auwidhat (Surat-an-Nas and Surat-al-Falaq). When his disease got aggravated, I used to recite them for him and blow (on his hands) and let him pass his hands over his body because of its blessing. (Ma`mar asked Ibn Shihab: How did he use to do Nafth? He said: He used to blow on his hands and then pass them over his face.)

Sahih al-Bukhari Book 76, Hadith 66