First of all, we’d like to state that Allah has permitted the fasting person to eat and drink until dawn comes. He, Most High, says: “… and eat and drink until the white thread becometh distinct to you from the black thread of the dawn …” (Al-Baqarah: 187)
Elaborating on this, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
“The exact cut off time for imsak (abstaining from food, drink, etc.) is the time of fajr; so if one ate until that time they did not incur any sin. Most of the time people confuse between the preferred time and the permissible one; the preferred time for imsak, according to scholars, is to finish sahur ten minutes before fajr. This ruling is based on a report from a Companion of the Prophet (peace and blessings be upon him): When asked what was the gap between the time they finished eating sahur with the Prophet (peace and blessings be upon him) and they prayed fajr, he said: “The gap between the two was sufficient enough for a person to read fifty verses of the Qur’an.” It is, however, wrong to conclude from this that we are not allowed to eat until arrival of fajr since Allah clearly states in the Qur’an, “Eat and drink until the white thread of dawn is distinct from the black thread (i.e., until the arrival of true dawn).”