The Prophet ﷺ was asked about the great sins He said, "They are:-- (1 ) To join others in worship with Allah, (2) To be undutiful to one's parents. (3) To kill a person (which Allah has forbidden to kill) (i.e. to commit the crime of murdering). (4) And to give a false witness."  

سُئِلَ النَّبِيُّ ﷺ عَنِ الْكَبَائِرِ قَالَ الإِشْرَاكُ بِاللَّهِ وَعُقُوقُ الْوَالِدَيْنِ وَقَتْلُ النَّفْسِ وَشَهَادَةُ الزُّورِ  

The Prophet ﷺ said thrice, "Should I inform you out the greatest of the great sins?" They said, "Yes, O Messenger of Allah ﷺ!" He said, "To join others in worship with Allah and to be undutiful to one's parents." The Prophet ﷺ then sat up after he had been reclining (on a pillow) and said, "And I warn you against giving a false witness, and he kept on saying that warning till we thought he would not stop. (See Hadith No. 7, Vol. 8)  

قَالَ النَّبِيُّ ﷺ أَلاَ أُنَبِّئُكُمْ بِأَكْبَرِ الْكَبَائِرِ ثَلاَثًا قَالُوا بَلَى يَا رَسُولَ اللَّهِ قَالَ الإِشْرَاكُ بِاللَّهِ وَعُقُوقُ الْوَالِدَيْنِ وَجَلَسَ وَكَانَ مُتَّكِئًا فَقَالَ أَلاَ وَقَوْلُ الزُّورِ قَالَ فَمَا زَالَ يُكَرِّرُهَا حَتَّى قُلْنَا لَيْتَهُ سَكَتَ