The Holy Prophet of Islam (peace be upon him and his progeny) said:
"إذا قَدَرْتَ عَلى عَدُوِّكَ فَاجْعَلِ الْعَفْوَ شُكْراً لِلقُدْرَةِ عَلَيْهِ"
When you overcome your enemy, adopt forgiveness and pardon as the gratitude for this victory.1
In Islam’s view, any favor and grace, without any exception, should be reciprocated by gratitude. For the gift of empowerment over the enemy, one expresses gratitude by forgiving the enemy . Victories become rooted only when enemy’s heart is purged of the spite and the root cause of the opposition is removed. Pardon will touch their hearts in a way that yesterday’s enemy becomes today’s friend. It is then that the victory is truly complete - outwardly and inwardly. Conversely, those who seek vengeance after victory not only deprive themselves from a great human virtue, but also endanger their victory.