A man’s reviling of his parents is one of the grave sins. He was asked : Messenger of Allah! How does a man revile his parents? He replied: He reviles the father of a man who then reviles his father, and he reviles a man’s mother and he reviles his.
قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ مِنْ أَكْبَرِ الْكَبَائِرِ أَنْ يَلْعَنَ الرَّجُلُ وَالِدَيْهِ قِيلَ يَا رَسُولَ اللَّهِ كَيْفَ يَلْعَنُ الرَّجُلُ وَالِدَيْهِ قَالَ يَلْعَنُ أَبَا الرَّجُلِ فَيَلْعَنُ أَبَاهُ وَيَلْعَنُ أُمَّهُ فَيَلْعَنُ أُمَّهُ