Messenger of Allah 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." Shuʿba (the sub-narrator) states that most probably the Prophet said, "the false witness."  

ذَكَرَ رَسُولُ اللَّهِ ﷺ الْكَبَائِرَ أَوْ سُئِلَ عَنِ الْكَبَائِرِ فَقَالَ الشِّرْكُ بِاللَّهِ وَقَتْلُ النَّفْسِ وَعُقُوقُ الْوَالِدَيْنِ فَقَالَ أَلاَ أُنَبِّئُكُمْ بِأَكْبَرِ الْكَبَائِرِ قَالَ قَوْلُ الزُّورِ أَوْ قَالَ شَهَادَةُ الزُّورِ قَالَ شُعْبَةُ وَأَكْثَرُ ظَنِّي أَنَّهُ قَالَ شَهَادَةُ الزُّورِ  

I heard Anas b. Malik saying: The Messenger of Allah ﷺ talked about the major sins, or he was asked about the major sins. Upon this he observed: Associating anyone with Allah, killing of a person, disobedience to parents. He (the Prophet further) said: Should I not inform you about the gravest of the major sins, and (in this connection) observed: False utterance or false testimony. Shu'ba said. It was most probably" false testimony".  

ذَكَرَ رَسُولُ اللَّهِ ﷺ الْكَبَائِرَ أَوْ سُئِلَ عَنِ الْكَبَائِرِ فَقَالَ الشِّرْكُ بِاللَّهِ وَقَتْلُ النَّفْسِ وَعُقُوقُ الْوَالِدَيْنِ وَقَالَ أَلاَ أُنَبِّئُكُمْ بِأَكْبَرِ الْكَبَائِرِ قَالَ قَوْلُ الزُّورِ أَوْ قَالَ شَهَادَةُ الزُّورِ قَالَ شُعْبَةُ وَأَكْبَرُ ظَنِّي أَنَّهُ شَهَادَةُ الزُّورِ  

"الْكَبَائِرُ: الشِّرْكُ باللهِ، وقَتْلُ النَّفْسِ، وَعقُوقُ الْوَالِدْين، ألا أُنَبِّئُكُمْ بأَكبَر الْكَبَائِر؟ قَوْلُ الزُّورِ، أوْ شَهَادَةُ الزُّورِ" .