It is narrated from Hazrat Anas bin Malik (may Allah be pleased with him) that a person asked the Prophet (peace and blessings be upon him) about the time of Fajr. So the Prophet (peace and blessings be upon him) instructed Hazrat Bilal (may Allah be pleased with him) at the time of the rising of Fajr and the prayer was established. Then the next day, he led the prayer when it was quite bright and said, "Where is the one who asked about the time of Fajr prayer?" The time for Fajr prayer is between these two times.