May one establish the fajr prayer before dawn?
The time for the fajr prayer starts from the rise of fajr al-sadiq, which is the time when the dawn breaks, and lasts until the rise of the sun. Therefore, fajr time, in other words, the time to start fasting prohibitions, starts with fajr al-sadiq, that is to say, when the dawn breaks. It is stated in the Holy Qur’an, “It has been made permissible for you the night preceding fasting to go to your wives [for sexual relations]. So now, have relations with them and seek that which Allah has decreed for you [i.e., offspring]. And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the night [i.e., sunset].” (Baqarah, 2/187). As the time of fajr prayer starts with imsak (dawn), the fajr prayer can be performed after dawn. On the other hand, Hanafis find it more appropriate (mustahab) to establish it a while later (close to sunrise in isfar time) on grounds of some narratives about the subject (Ibn al-Humam, Fath, I, 227; Ibn Qudamah, al-Mughni, II, 29-30; Zaylai, Tabyin, I, 82). Indeed, the Prophet Muhammad also recommended this (Tirmidhi, Salat, 5).
The time of the fajr prayer lasts until the sun rises. Because according to the hadith regarding Gabriel’s leading the Prophet (saw) in prayer, he led the fajr prayer at dawn on the first day, and at a time close to sunrise and when it was day light on the second day, and said, “It is time for you and your ummah to establish fajr prayer between these two times.” (Tirmidhi, Salat, 1; Nasa’i, Mawaqit, 5,9; Muwatta, Wuqut, 3)
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS