Is Fajr prayer valid if performed an hour before its prescribed time, given that the Messenger (peace be upon him) used to pray it during the time of ghalas (darkness before dawn) or isfirar (when the sky begins to lighten), and Allah Almighty says: "Indeed, prayer has been decreed upon the believers a book [at] fixed times," and among the conditions for prayer's acceptance is the entry of its time?

The Ummah has unanimously agreed that the time for Fajr prayer begins with the appearance of the true dawn (the second dawn) and extends until sunrise. The true dawn is the light that spreads horizontally across the horizon and increases in brightness. It differs from the false dawn, which appears as a vertical streak and then disappears. It is preferred to pray Fajr in the time of ghalas (the early part of its time), and it has been authentically reported that the Prophet, peace and blessings be upon him, used to pray it at that time. It has not been authentically reported that the Prophet, peace and blessings be upon him, delayed Fajr until isfar (when the light spreads significantly) except on one occasion. One of the conditions for the validity of prayer is the entry of its time, and the questioner must verify that the time has entered before praying.