Can the morning prayer (fajr) be performed as soon as the time for imsak begins?

The time for the morning prayer (fajr) begins with the appearance of the second dawn (true dawn), which is when the horizon starts to lighten, and continues until sunrise. Accordingly, the time of imsak, in other words, the time when fasting prohibitions begin, is the occurrence of the true dawn (fecr-i sâdık), that is, when the horizon starts to brighten. In the Qur'an, it is stated: "So now, have relations with them and seek what Allah has decreed for you. 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 sunset." (al-Baqara, 2/187). Since the time for the morning prayer begins with imsak, the morning prayer can be performed at this time. However, based on some related narrations, the Hanafi scholars considered it more appropriate (mustahabb) to delay it slightly and perform it at the time of isfar (when the horizon is brighter). (Ibn al-Humam, Fath al-Qadir, 1/225; Ibn Qudama, al-Mughni, 1/286; Zayla'i, Tabyin, 1/82) Indeed, the Prophet himself also recommended this. (Tirmidhi, Salat, 117 [154])

The time for the morning prayer continues until sunrise. According to the narration about Gabriel (Jibril) leading the Prophet (peace be upon him) in prayer, Gabriel led the morning prayer on the first day when the dawn broke, and on the second day when it was brighter and close to sunrise, and said: "This is the time of (prayer) for the prophets before you, and the time (for prayers) is between these two times." (Abu Dawud, Salat, 2 [393]; Tirmidhi, Salat, 113 [149]).

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu