Question: I would like Your Eminence to clarify the meaning of Imsak. Is it only a commendable act, or are all Muslims required to abide by it? Is it true that the Messenger of Allaah (peace be upon him) specified the time of Imsaak as being equal to the recitation of fifty Aayaahs (Qur’aanic verses) before Fajr (Dawn) Prayer? Scholars estimated it to be half an hour. What is the ruling on whoever eats or drinks while the Adaan (call to Prayer) for Fajr is being announced? Does Sawm (Fast) start upon hearing the Adaan for Fajr Prayer, or half an hour before Adaan, or after the Adaan is announced?
Answer: Imsaak means abstention from food and drink and all that invalidates Sawm from the beginning of the appointed time of Sawm. Allaah (Glorified and Exalted be He) clarifies in the Glorious Qur’aan the starting time of Sawm, which is the break of dawn, saying: …and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Sawm (fast) till the nightfall. The Adaan for Fajr Prayer is a proclamation of the break of dawn. Therefore, you have to stop eating and drinking when you hear it…. read more here.