Abdur Rahman bin A’ish, who is a companion of the Prophet (peace be upon him), states:“There are two types of dawn. One is that which spreads vertically in the sky; this does not prevent a person from eating suhoor, and it is not permissible to perform the (Fajr) prayer at this time. But when it spreads horizontally, then eating (suhoor) becomes forbidden and at that time you may perform the morning prayer.”This narration is authentic.