Hisham bin Urwah narrates from his father, who narrates from Sayyidah Aishah (may Allah be pleased with her), that Allah Almighty would wake the Prophet (peace and blessings be upon him) at night, and before the time of suhur came he (peace and blessings be upon him) would have finished his portion.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4658