Miswar bin Makhramah (may Allah be pleased with him) said: The spoils of al-Qadisiyyah were brought to Umar bin al-Khattab (may Allah be pleased with him), and on seeing them he began to weep. Abdur-Rahman bin Awf (may Allah be pleased with him) was with him; he said: Why are you weeping? This day is a day of joy. He said: Yes, but this has never been brought (to a people) except that it instils enmity and hatred among them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13034