To be undutiful to parents is one of the greatest sins
حَدَّثَنِي مُحَمَّدُ بْنُ الْوَلِيدِ، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، قَالَ حَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ أَبِي بَكْرٍ، قَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ ـ رضى الله عنه ـ قَالَ ذَكَرَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْكَبَائِرَ، أَوْ سُئِلَ عَنِ الْكَبَائِرِ فَقَالَ " الشِّرْكُ بِاللَّهِ، وَقَتْلُ النَّفْسِ، وَعُقُوقُ الْوَالِدَيْنِ ". فَقَالَ " أَلاَ أُنَبِّئُكُمْ بِأَكْبَرِ الْكَبَائِرِ ـ قَالَ ـ قَوْلُ الزُّورِ ـ أَوْ قَالَ ـ شَهَادَةُ الزُّورِ ". قَالَ شُعْبَةُ وَأَكْثَرُ ظَنِّي أَنَّهُ قَالَ " شَهَادَةُ الزُّورِ ".
Narrated Anas bin Malik: Allah's Messenger (ﷺ) mentioned the greatest sins or he was asked about the greatest sins. He said, "To join partners in worship with Allah; to kill a soul which Allah has forbidden to kill; and to be undutiful or unkind to one's parents." The Prophet (ﷺ) added, "Shall I inform you of the biggest of the great sins? That is the forged statement or the false witness." Shu`ba (the sub-narrator) states that most probably the Prophet said, "the false witness."