The Messenger of Allah ﷺ said, "Eat and drink, and do not let the rising vertical light alarm you. Eat and drink until the red light spreads across the horizon before you."
حدثنا هناد حدثنا ملازم بن عمرو حدثني عبد الله بن النعمان عن قيس بن طلق
أن رسول الله ﷺ قال كلوا واشربوا ولا يهيدنكم الساطع المصعد وكلوا واشربوا حتى يعترض لكم الأحمر
[Its chain of transmission is hasan]. Abu Dawud narrated it in the Book of Fasting, chapter on the time of suhur, hadith 2348, from the hadith of Mulazim, with the same wording, and Ibn Khuzayma graded it sahih, 1930.There are also narrations on this subject from Adi bin Hatim [coming up: 2971], Abu Dharr [Tahawi in Maani al-Athar, 1/140], and Samura [coming up: 706].