'Aayesh Radiyallahu 'Anha say "Rasulullah Sallallhu 'Alayhi Wasallam performed eleven rak'ahs at night, of which one was a rak'ah of witr. When he completed this he slept on the right side" (ID)
English reference (ID): Book 39, Hadith 258 (ID)
Arabic reference (ID): Book 40, Hadith 271 (ID)