Is it necessary to repeat fasting the days that were fasted in Ramadan and during qada' (making up missed fasts), if there was negligence in prayer during those days?

Abandoning prayer is considered one of the greatest sins and major transgressions, and its perpetrator is exposed to Allah's punishment and wrath. Muslims do not differ on the sinfulness of one who abandons prayer, as Ibn al-Qayyim stated in his book, "Al-Salah."

Scholarly opinions differed regarding the ruling on the fasting of one who abandons prayer. Those who stated that abandoning prayer out of laziness does not constitute disbelief (kufr) affirmed the validity of his fasting and that he is not obligated to make up for it. Those who stated that it constitutes disbelief held that fasting or any other act of obedience would not benefit him, and in this case, he is not obligated to make up for what he missed upon returning to Islam.

Based on this, there is no obligation to repeat the fast, but it is recommended to make up for the prayers that were missed.