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. (Using translation from Bukhārī 6675)
عَنِ النَّبِيِّ ﷺ قَالَ «الْكَبَائِرُ الْإِشْرَاكُ بِاللهِ وَعُقُوقُ الْوَالِدَيْنِ وَقَتْلُ النَّفْسِ وَالْيَمِينُ الْغَمُوسُ»