What is imsak? When does it start? May one continue to eat and drink for a short while when the adhan for fajr prayer starts to be recited?
Imsak, which literally means “to refrain, restrain, resign and abstain from”, as a religious term means to refrain and abstain from eating, drinking, sexual intercourse and other things that invalidate fasting from dawn (fajr al-sadiq) until the sunset (the time of iftar). Iftar is the opposite of imsak.
Among the people, “imsak” is used to mean the time when fasting begins. In this regard, imsak is the time to begin fasting.
The time to begin and finish fasting is described in the Qur’an as: “And (at Ramadan nights) eat and drink, until the white thread of dawn appear to you (when dawn breaks/fajr al-sadiq) distinct from its black thread; then complete your fast (without eating, drinking, and sexual intercourse) till the night appears.” (Baqarah, 2/187)
The imsak time shown on calendars describes the time to begin fasting. Imsak is also the moment when the night ends, the time for ‘isha prayer ends and that of fajr prayer begins. The adhan starts to be recited with the beginning of imsak time. Therefore, one needs to stop eating and drinking with the beginning of adhan. But one may swallow the piece in the mouth when the adhan starts to be recited.
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS