'Aayeshah Radiyallahu 'Anha narrates:
"Every night before Rasulullah Sallallahu 'Alayhi Wasallam slept on his bed, he put together his hands (as in the du'aa) and blew on it and recited (the surahs of) AI-Ikhlaas (Qul huwauahu ahad), AI-Falaq (Qul a'udhu birabbil falaq), and An-Naas (Qui a'udhu birabbin naas) and wiped those parts of the body that he could (wherever the hand could reach). He began with the head, then the face and then the front part of his body. This was done thrice".
English reference: Book 38, Hadith 244
Arabic reference: Book 39, Hadith 257