Musnad Abu Ya'la al-Mawsili 89:1

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Abd al-Qahir ibn al-Sari al-Sulami narrated to us, Ibn Kinanah ibn al-Abbas ibn Mirdas al-Sulami narrated to me, that his father narrated to him, from his father, al-Abbas: That the Messenger of Allah (may Allah bless him and grant him peace) prayed on the evening of Arafah for his Ummah for forgiveness and mercy, and he supplicated much. Allah answered him, "I have done so, and I have forgiven your Ummah, except for the oppression of some of them against others." He repeated the supplication and said, "O Lord, You are able to forgive the oppressor and reward the oppressed with better than what he was oppressed for." But he was not answered regarding that on that evening. When it was the next day, he prayed in the morning at Muzdalifah, and he returned to supplicating for his Ummah. The Prophet (may Allah bless him and grant him peace) did not delay before he smiled. Some of his companions said, "O Messenger of Allah, may my father and mother be sacrificed for you, you smiled at a time when you would not usually laugh, so what made you laugh? May Allah make your teeth shine." He said, "I smiled at the enemy of Allah, Iblis, when he knew that Allah had answered me regarding my Ummah and forgiven the oppressor. He rushed, calling out for destruction and woe, and throwing dust upon his head." He said once, "So I laughed at his distress."