Does ridiculing the committed—even if it's a slip of the tongue, or done in a state of anger or jest—nullify good deeds, and what is the path to sincere repentance and avoiding the nullification of deeds?

Whoever mocks those who adhere to the religion of Allah and fulfill His commands exhibits a form of hypocrisy. If their mockery stems from the adherents' adherence to the Shari'ah, then their mockery of the Shari'ah constitutes disbelief (kufr). However, if they mock them and intend to target their persons and dress, irrespective of their adherence to the Sunnah, then they do not become disbelievers thereby, but they are in great danger. Mocking those who adhere to the commands of Allah and His Messenger, merely because they adhere to them, is forbidden and extremely dangerous. It is feared that their dislike for them stems from a dislike of their uprightness in the religion of Allah, making their mockery of them a mockery of the path they are on. Whoever regrets such actions must repent and seek forgiveness, for Allah forgives all sins. They must also seek forgiveness from those they have wronged. If they are unable to do so, they should seek forgiveness for them, pray for their well-being, and mention them positively to compensate for what has transpired. They should also strive to replace their evil deeds with good ones by upholding the banner of the Sunnah and adhering to the Prophetic guidance, outwardly and inwardly.