Sahih Bukhari
Prayer at Night (Tahajjud)
Volume: 002 / Book Number: 021 / Hadith Number: 256
Narrated 'Aisha;
Allah's Apostle offered the 'Isha' prayer (and then got up at the Tahajjud time) and offered eight Rakat and then offered two Rakat while sitting. He then offered two Rakat in between the Adhan and Iqama (of the Fajr prayer) and he never missed them.