What is the wisdom behind delaying the two Rak'ahs of Fajr (Sunnah) prayer until the sun has risen to the height of a spear, even though the noble Hadith, "Whoever sleeps through a prayer or forgets it, let him pray it when he remembers it or wakes up," indicates that a missed prayer should be performed immediately upon waking?

"Whoever misses the Sunnah prayer of Fajr, it is better for them to pray it after the sun has risen, based on the saying of the Prophet, peace and blessings be upon him: 'Whoever has not prayed the two Rak'ahs of Fajr, let him pray them after the sun has risen.' It is also permissible to make them up after the obligatory prayer and before sunrise, based on the action of Qais ibn Fahd and the Prophet's, peace and blessings be upon him, approval of it."