Can actions that appear to be an insult to the Prophet, peace and blessings be upon him, and seem deliberate, be involuntary due to a weak resistance to whispered [evil] suggestions (waswas)? And for someone who curses the religion, and is accustomed to cursing everything, is it obligatory for him to repent only from cursing the religion to return to Islam, or must he repent from everything he curses?

The door of repentance is open for all sins. Repentance and remorse are linked to the servant abandoning the sin and ceasing from it. One must avoid getting carried away by whispers (waswasah), mocking religion, and cursing, and turn away from thinking about these matters. Occupy yourself with learning religious knowledge and participating in social and da'wah (preaching) activities. Avoid isolation and associate with good company.