Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.130A.

Section : Fasting, what would fulfil the sunnah of eating a pre-dawn meal.

The sunnah would be fulfilled by eating a small or large quantity of food, or even just by drinking a sip of water. Abu Sa’id al-Khudri reported that the Messenger of Allah said: “The pre-dawn meal is blessed, so do not neglect it even if you only take a sip of water. Verily, Allah and the angels pray for those who have pre-dawn meals.” This is related by Ahmad.