Sahih Al Bukhari Hadith Number 1159

Narrated `Aisha;: Allah’s Messenger (peace be upon him) offered the `Isha’ prayer (and then got up at the Tahajjud time) and offered eight rak`at and then offered two rak`at while sitting. He then offered two rak`at in between the Adhan and Iqama (of the Fajr prayer) and he never missed them.

19  Prayer at Night (Tahajjud)
Hadith number 1159
Volume no 2
Chapter: 22 ( Regularity of two Rak’a (Sunna) of the Fajr)