'A'isha reported Allah's Messenger as saying: "The two rak'ahs at dawn (Sunnah of Fajr) are better than this world and what it contains."
In another narration: "They are dearer to me than the whole world." (Saheh Muslim, 725)
The two rak'ahs at dawn are the sunnah of fajr. If this is the rank of the sunnah of fajr, what would be the rank of the obligatory prayer then!!