Musannaf Ibn Abi Shayba 33:221

'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, from Ibrahim ibn 'Abd al-Rahman ibn 'Awf, who said: When the treasures of the family of Chosroes were brought to 'Umar, there was among the gold and silver that which almost dazzled the sight. 'Umar wept at that. 'Abd al-Rahman said: "What makes you weep, O Commander of the Faithful? This day is a day of gratitude, happiness, and joy." 'Umar said: "This has never increased among a people except that Allah cast enmity and hatred among them."