The Prophet ﷺ said, "The biggest sins are: To join others in worship with Allah; to be undutiful to one's parents; to kill somebody unlawfully; and to take an oath Al-Ghamus.
عَنِ النَّبِيِّ ﷺ قَالَ الْكَبَائِرُ الإِشْرَاكُ بِاللَّهِ وَعُقُوقُ الْوَالِدَيْنِ وَقَتْلُ النَّفْسِ وَالْيَمِينُ الْغَمُوسُ