Musnad Ahmad 290:1

Abdullah ibn Ahmad said: Ibrahim ibn al-Hajjaj al-Naji narrated to me, saying: Abd al-Qahir ibn al-Sari narrated to us, from Ibn Kinanah ibn Abbas ibn Mirdas, from his father, that his father, al-Abbas ibn Mirdas, narrated to him that the Messenger of Allah (may Allah bless him and grant him peace) prayed on the evening of Arafah for his nation for forgiveness and mercy, and he supplicated much. Allah (Mighty and Majestic is He) answered him: "I have done so, and I have forgiven your nation, except for those who have wronged one another." He said: "O Lord, You are capable of forgiving the oppressor and rewarding the oppressed with better than what they were wronged for." But he did not receive an answer to that on that evening. When it was the next day, he prayed in the morning at Muzdalifah, and he returned to supplicating for his nation. 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 laughed at a time you would not usually laugh, so what made you laugh? May Allah make your teeth laugh (keep you happy)." He said: "I smiled at the enemy of Allah, Iblis, when he learned that Allah (Mighty and Majestic is He) had answered me regarding my nation and forgiven the oppressor. He stooped down, calling for destruction and woe, and throwing dust upon his head, so I smiled at his panic over what he was doing."