Hadith 4:199
Abu Dawud al-Tayalisi narrated to us, from Yazid ibn Zayd, who said: I heard al-Hasan, and a man said to him: "I eat the pre-dawn meal (suhur) while I am in doubt about the dawn." He said: "Eat as long as you are in doubt, for by Allah, the dawn is not hidden."
حدثنا أبو داود الطيالسي عن يزيد بن زيد قال سمعت الحسن وقال له رجل أتسحر وامتري في الصبح فقال كل ما امتريت انه والله ليس بالصبح خفاء