[Al-Qur'an 5:28]: "If you do stretch your hand against me to kill me, I shall never stretch my hand against you to kill you, for I fear Allah; the Lord of the 'Alamin (mankind, jinns, and all that exists)."
After both brothers, Habil and Qabil, presented their sacrifices to Allah, only Habil's was accepted.
Qabil, filled with jealousy and anger, is outraged due to his sacrifice being rejected and threatens to murder his brother.
Habil refrained from counter attacking his brother's evil deed of killing him due to his fear of Allah.
Overwhelmed by rage and humiliation, Qabil carries out the unthinkable act of killing Habil, marking the first murder committed by mankind on earth.
After Qabil kills his brother Habil, Qabil experiences panic, fear and regret.
Qabil was unsure of how to hide his brother's body.
Allah sent a crow which pecked on the ground. This was a sign to show him what to do with the body of Habil, and inevitably, how mankind would also bury their dead.
Once realising this, Qabil became from among those who regretted.