This is from Rambam Halachot Teshuva: (From Chabad.org)
Anyone who changes his mind about the mitzvot he has performed and regrets the merits [he has earned], saying in his heart: "What value was there in doing them? I wish I hadn't performed them" - loses them all and no merit is preserved for him at all as [Ezekiel 33:12] states "The righteousness of the upright will not save him on the day of his transgression." This only applies to one who regrets his previous [deeds].
Do any sources discuss how one can get back the reward for Mitzvot that he regretted? If so, how? Please try to cite sources. Thank you so much!
