It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) would offer the two rak'ahs of Fajr; if I was awake, he would talk with me, otherwise he (peace and blessings be upon him) would also lie down until he (peace and blessings be upon him) stood up for the prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3035