﴿ فَطَوَّعَتْ لَهُۥ نَفْسُهُۥ قَتْلَ أَخِيهِ فَقَتَلَهُۥ فَأَصْبَحَ مِنَ ٱلْخَٰسِرِينَ ﴾

“But the other's passion drove him to slaying his brother; and he slew him: and thus he became one of the lost.”

(But (the other's) mind imposed on him) his ego permitted him (the killing of his brother, so he slew him and became one of the losers) who deserved punishment.