Are parents cast out from God's mercy if their son curses them, or if someone else curses their parents, and will they be punished in the Hereafter for the son's sin?

Cursing is dangerous, and it does not affect the cursed unless he deserves it; otherwise, the curse returns upon the one who utters it. If someone curses or reviles Abu Muslim, and the other person then curses his father, the first person is sinful twice: first, for reviling and cursing the father of his companion, and second, for causing his own father to be cursed.