What is the ruling regarding someone who, out of ignorance, delayed the Fajr prayer, then believed that he had left the fold of Islam, and so began intentionally delaying prayers, intending to re-enter Islam? What is incumbent upon him?

One who delays the Fajr prayer out of ignorance of the ruling does not become an infidel, especially since the majority of scholars do not consider one who abandons prayer entirely and intentionally an infidel, as long as he does not deny its obligatory nature.