Abu Dawud Book 2, Hadith Number 1257.

Chapter : On lying after praying the two rakahs before the dawn prayer.

Narated By ‘Aisha : When the Apostle of Allah (PBUH) finished his prayer late in the night, he would see. If I was awake, he would talk to me. If I was sleeping, he would awaken me, and pray two rak’ahs, then he would lie down as long as the muadhdhdin came to him and called him for the dawn prayer. Then he would pray two rak’ahs lightly and come out for the prayer.