Sahih Bukhari Volume 006, Book 060, Hadith Number 094.
Narrated By Ibn Abbas : (One night) I stayed overnight in the house of my aunt Maimuna, and said to myself, "I will watch the prayer of Allah's Apostle " My aunt placed a cushion for Allah's Apostle and he slept on it in its length-wise direction and (woke-up) rubbing the traces of sleep off his face and then he recited the last ten Verses of Surat-al-Imran till he finished it. Then he went to a hanging water skin and took it, performed the ablution and then stood up to offer the prayer. I got up and did the same as he had done, and stood beside him. He put his hand on my head and held me by the ear and twisted it. He offered two Rakat, then two Rakat, then two Rakat, then two Rakat, then two Rakat, then two Rakat, and finally the Witr (i.e. one Rak'a) prayer.