Muhammad bin Abdur Rahman narrates: The Prophet Muhammad (peace be upon him) said: "There are two types of true dawn (Subh Sadiq). One is the true dawn that spreads like the tail of a snake (horizontally), at which time it is not permissible to perform (the Fajr prayer), and it is not forbidden for the one taking suhoor to eat. However, the (light) that spreads vertically on the horizon makes (the Fajr) prayer permissible (i.e., the time for prayer begins), and makes eating for the one taking suhoor forbidden (i.e., the time for suhoor ends at that moment)."