فَطَوَّعَتْ لَهُۥ نَفْسُهُۥ قَتْلَ أَخِيهِ فَقَتَلَهُۥ فَأَصْبَحَ مِنَ ٱلْخَٰسِرِينَ
Asad Quran Translation
But the other's passion37
drove him to slaying his brother; and he slew him: and thus he became one of the lost.
Among the many meanings attributable to the noun nafs (primarily, "soul", or "mind", or "self"), there is also that of "desire" or "passionate determination" (Qamus, see also Zamakhshari's Asas); in this context, the best rendering seems to be "passion".
Malik Quran Translation
The latter's soul prompted him to kill his brother; he killed him and thus became one of the losers.
Yusuf Ali Quran Translation
The (selfish) soul of the other led him to the murder of his brother: he murdered him and became (himself) one of the lost ones. 734
The innocent unselfish pleading of the younger brother had no effect, for the soul of the other was full of pride, selfishness and jealousy. He committed the murder, but in doing so, ruined his own self.
Mustafa Khattab Quran Translation
Yet Cain convinced himself to kill his brother, so he killed him—becoming a loser.
Piktal Quran Translation
But (the other's) mind imposed on him the killing of his brother, so he slew him and became one of the losers.
FatawwaAAat lahu nafsuhu qatla akheehi faqatalahu faasbaha mina alkhasireena