Abdullah bin Qatadah (may Allah have mercy on him) says: On the day of Nahrawan I was among the horsemen with Sayyiduna Ali (may Allah be pleased with him). When he had finished the battle, he did not cut off any head nor uncover anyone's private parts ('awrah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16758