Q. 429. We have seen in some calendars that during Ramadan there is a section called Al-Imsak. It is situated about ten minutes or a quarter of an hour before the Fajr prayer. Is there any basis for this in the Sunnah, or is it an innovation? Deliver a legal verdict for us and may you be rewarded.
A. This is a form of innovation, and there is no basis for it in the Sunnah. Indeed, the Sunnah contradicts it, because Allah says in His Mighty Book:
“. . .and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night)” 
And the Prophet (صلى الله عليه وسلم) said;
“Bilal makes the Athan at night, so eat and drink until you hear the Athan of Ibn Umm Maktum, because he does not call the Athan until Fajr begins.” 
This Imssak (time to stop eating and drinking) which some people regulate is an addition to what Allah, the Almighty, the All-Powerful has enjoined, and so it is invalid and it is extreme, and the Prophet (صلى الله عليه وسلم) said:
“Ruined are those who indulge in extremism, ruined are those who indulge in extremism, ruined are those who indulge in extremism.” 
 Al-Baqarah 2:187
 Reported by Al-Bukhari in the Book of Fasting, in the Chapter: The Statement of the Prophet (صلى الله عليه وسلم) “Do not Let the Athan of Bilal Prevent You” (1918); and by Muslim in the Book of Fasting, in the Chapter: Clarification That Fasting Starts With the Beginning of Fajr (1092).
 Reported by Muslim in the Book of Fasting, in the Chapter: Ruined are Those Who Indulge in Tanattu’ (2670).
From the Book “Fatawa Arkanul-Islam “
Islamic Verdicts on the Pillars of Islam (Volume Two)
By the Honorable Shaikh Muhammad bin Salih Al- ‘Uthaimeen
Ramdhan & Fasting Index Page – https://abdurrahman.org/ramadhan/