Is it obligatory to make up two Ramadans for someone who abandoned prayer during them after puberty, knowing that fasting is not accepted without prayer, then repented and returned to prayer?

Abandoning prayer is one of the gravest major sins. The works of one who abandons prayer may be nullified, based on the Prophet's (peace and blessings be upon him) saying: "Whoever misses the 'Asr prayer, his deeds are nullified." The nullification of deeds may be complete for one who abandons prayer entirely, or partial for one who misses a specific prayer. Nevertheless, the door to repentance is open. According to the majority of scholars, a complete repentance includes making up the missed prayers. As for fasting, it remains valid and does not need to be made up.