Does the penitent who turns to the remembrance of Allah after a long heedlessness regret what he missed of remembrance, or not? And what should he do to avoid regret on the Day of Resurrection?

It is part of Allah's mercy towards His servants that whoever repents and performs righteous deeds, Allah accepts his repentance and transforms his evil deeds into good ones, as stated in His glorious words: "Except for those who repent, believe and do righteous work. For them Allah will change their evil deeds into good ones. And ever is Allah Forgiving and Merciful." The best way for a repentant person to compensate for the good deeds he missed is to persistently engage in the remembrance of Allah. Imam Malik narrated from Abu al-Darda' that the Prophet, peace and blessings be upon him, said: "Shall I not inform you of the best of your deeds, the purest in the sight of your King, the highest in your ranks, better for you than giving gold and silver, and better for you than meeting your enemy and striking their necks and them striking your necks?" They said: "Yes, O Messenger of Allah." He said: "The remembrance of Allah." If the hadith "The people of Paradise will not regret anything except a moment that passed them in which they did not remember Allah" is authentic, then the regret mentioned in it is general for anyone who was heedless of the remembrance of Allah. The regret mentioned for the people of Paradise – if authentic – would be in the Standing (on the Day of Judgment) and not in Paradise itself.