Sahih Bukhari Volume 001, Book 011, Hadith Number 665.
Narated By Ibn 'Abbas : Once I passed the night in the house of my aunt Maimuna. Allah's Apostle offered the 'Isha' prayer and then came to the house and offered four Rakat an slept. Later on, he woke up and stood for the prayer and I stood on his left side. He drew me to his right and prayed five Rakat and then two. He then slept till I heard him snoring (or heard his breath sounds). Afterwards he went out for the morning prayer.