What is the ruling on one who secretly curses his father due to his stinginess and reliance on his employed wife?

If Allah has forbidden merely saying "uff" to one's parents, then it is even more prohibited to insult or curse them, even if the insult is secret or due to the father's stinginess. This is because honoring parents is obligatory, even if they are disbelievers. Insulting parents is an act of disobedience (uquq) and a sign of abandonment (khidhlan), and Allah may hasten the punishment for this sin in this world before the Hereafter.