The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1036
'A'isha reported: The Apostle of Allah (may peace be upon him) said his whole prayer (Tahajjud prayer) during the night while I lay between him and the Qibla. When he intended to say Witr (prayer) he awakened me and I too said witr (prayer).