Abu Dawud Book 2, Hadith Number 1258.
Chapter : On lying after praying the two rakahs before the dawn prayer.
Narated By ‘Aisha, Ummul Mu’minin : When the Prophet (PBUH) prayed the two rak’ahs of the dawn prayer, he would lie down if I was asleep; in case I was awake, he would talk to me.