Surah Al-Ma'idah (5:30)

فَطَوَّعَتْ لَهُۥ نَفْسُهُۥ قَتْلَ أَخِيهِ فَقَتَلَهُۥ فَأَصْبَحَ مِنَ ٱلْخَٰسِرِينَ

So then his self made the killing of his brother seem easy to him, and he killed him, and thus he became one of the losers.