Sahih Bukhari Volume 002, Book 021, Hadith Number 223.

Narated By 'Aisha : Allah's Apostle used to offer eleven Rakat and that was his prayer. He used to prolong the prostration to such an extent that one could recite fifty verses (of the Quran) before he would lift his head. He used to pray two Rakat (Sunna) before the Fajr prayer and then used to lie down on his right side till the call-maker came and informed him about the prayer.