Narrated Ibn 'Abbas:

For the children of Israel the punishment for crime was Al-Qisas only (i.e., the law of equality in punishment) and the payment of Blood money was not permitted as an alternate. But Allah said to this nation (Muslims): 'O you who believe! Qisas is prescribed for you in case of murder, .....(up to) ...end of the Verse. (2.178) Ibn 'Abbas added: Remission (forgiveness) in this Verse, means to accept the Blood-money in an intentional murder. Ibn 'Abbas added: The Verse: 'Then the relatives should demand Blood-money in a reasonable manner.' (2.178) means that the demand should be reasonable and it is to be compensated with handsome gratitude.

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ كَانَتْ فِي بَنِي إِسْرَائِيلَ قِصَاصٌ، وَلَمْ تَكُنْ فِيهِمُ الدِّيَةُ فَقَالَ اللَّهُ لِهَذِهِ الأُمَّةِ {كُتِبَ عَلَيْكُمُ الْقِصَاصُ فِي الْقَتْلَى} إِلَى هَذِهِ الآيَةِ {فَمَنْ عُفِيَ لَهُ مِنْ أَخِيهِ شَىْءٌ}. قَالَ ابْنُ عَبَّاسٍ فَالْعَفْوُ أَنْ يَقْبَلَ الدِّيَةَ فِي الْعَمْدِ، قَالَ {فَاتِّبَاعٌ بِالْمَعْرُوفِ} أَنْ يَطْلُبَ بِمَعْرُوفٍ وَيُؤَدِّيَ بِإِحْسَانٍ.