Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
The time of the morning (Fajr) prayer begins with the true dawn and lasts until sunrise.
In his famous work, Fiqh As-Sunnah, Sheikh Sayyid Sabiq, elaborates on the subject as follows:
The time of the morning (Fajr) prayer begins with the true dawn and lasts until sunrise. It is preferred to pray Fajr early in its permissible time.
Abu Mas`ud al-Ansari (may Allah be pleased with him) reported that the Messenger of Allah (peace be upon him) prayed the Fajr prayer in the darkness (of the dawn).
Another time, he prayed Fajr when the dawn was shining (or glowing). Then after that, he always prayed in the darkness (of the dawn) until he died.” (Related by Abu Dawud and al-Baihaqi. Its chain is sahih.)
`Aishah (may Allah be pleased with her) said: “Believing women would pray the Fajr prayer with the Prophet (peace be upon him) being enveloped in their clothing. They would return to their homes after the prayer and no one could recognize them due to the darkness (of the dawn).” (Related by “the group.”)
Rafi` ibn Khadeej (may Allah be pleased with him) related a hadith in which the Prophet (peace be upon him) said, “Make the Fajr prayer at daybreak, as your reward will be greater.”
In another version it states, “Make the morning prayer at the shining (time of the dawn), as your reward will be greater.” (Related by “the five.” At-Tirmidhi and Ibn Hibban grade it as sahih.)
It refers to the time that one finishes the prayer, not the time when one begins it. That is, one should make the recital long so that one is in prayer until the dawn becomes “shiny.” This is what the Prophet (peace be upon him) used to do, for he would recite between 60 and 100 verses. It also means to make sure that the dawn has come.
Almighty Allah knows best.