The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1608
Abu Salama asked 'A'isha about the prayer of the Messenger of Allah (may peace be upon him) She said: He observed thirteen rak'ahs (in the night prayer). He observed eight rak'ahs and would then observe Witr and then observe two rak'ahs sitting, and when he wanted to bow he stood up and then bowed down, and then observed two rak'ahs in between the Adhan and lqama of the dawn prayer.