One of the very good things in Ramadan is sahur (Arabic for: meal before fasting). It is a sunnah of Prophet Muhammad (peace and blessings be upon him). More than one hadith referred to sahur,“The difference between our fasting and that of the People of the Book is sahur (Muslim).
a Muslim should be alert regarding the deadline of sahur, as one could lose his or her fasting if still eating and the fasting for the day has already begun. A Muslim is allowed to eat up till the time for Fajr Prayer, but once the call to prayer has been made, he or she should stop eating.

Dr. Muzammil H. Siddiqi, president of the Fiqh Council of North America, stated: You can eat up to the time of Fajr Prayer. Almighty Allah says in the Qur’an, [Eat and drink until the white thread of dawn becomes distinct from the black thread (of night)] (Al-Baqarah 2:187). In an authentic hadith, the Prophet (peace and blessings be upon him) said, “Eat and drink until Ibn Umm Maktum [the caller to Prayer at the time] gives the adhan [Arabic for: call for the Prayer].” Ibn Umm Maktum was a blind man, and he used to give adhan after people tell him that the dawn has appeared. It is good to eat until the last minute until F ajr starts as the Prophet (peace and blessings be upon him) said, “My community will remain following the balanced way as long as they make iftar (Arabic for: meal to break the fast) early and delay their sahur.”
Of course, one should be careful of the beginning and ending times of the fast. We are not allowed to eat in the time between Fajr and Maghrib (Arabic for: sunset).