What is the ruling on the action of a son who curses his mother (without her hearing him) because of her anger and her praying for death upon herself and her children?

It is not permissible for a mother to supplicate against her son. The son should gently advise her. Secretly cursing one's mother is a reprehensible act, for jurists have explicitly stated the prohibition of speaking to oneself about the faults of others. Indeed, negative suspicion is forbidden, just as negative speech is forbidden. As for fleeting thoughts, they are pardoned. Cursing a Muslim is a transgression, and a believer is not one who curses. The right of a mother is immense, and it is obligatory to honor her and obey her in what is good, even if she is abusive. Whoever repents and has good expectations of Allah, let him be gladdened by forgiveness.