Quran Surah Fussilat

و لَا تَستَوی الحَسَنَةُ وَ لَا السَیئَةُ ادفَع بِالَتی هِیَ اَحسَنُ فَاِذا الَذِی بَینَکَ وَ بَینَهُ عَدَاوَةُ کَاَنَهُ وَلِی حَمِیمُ

Good and evil [conduct] are not equal. Repel [evil] with what is best. [If you do so,] behold, he between whom and you was enmity, will be as though he were a sympathetic friend. 

Quran Surah Fussilat 41: 34