The Prophet ﷺ said, "The biggest of Al-Kaʿba'ir (the great sins) are (1) to join others as partners in worship with Allah, (2) to murder a human being, (3) to be undutiful to one's parents (4) and to make a false statement," or said, "to give a false witness."
عَنِ النَّبِيِّ ﷺ قَالَ الْكَبَائِرُ وَحَدَّثَنَا عَمْرٌو حَدَّثَنَا شُعْبَةُ عَنِ ابْنِ أَبِي بَكْرٍ عَنْ أَنَسِ بْنِ مَالِكٍ عَنِ النَّبِيِّ ﷺ قَالَ أَكْبَرُ الْكَبَائِرِ الإِشْرَاكُ بِاللَّهِ وَقَتْلُ النَّفْسِ وَعُقُوقُ الْوَالِدَيْنِ وَقَوْلُ الزُّورِ أَوْ قَالَ وَشَهَادَةُ الزُّورِ