Musannaf Ibn Abi Shayba 21:463

Qarrad Abu Nuh narrated to us, 'Ikrimah ibn 'Ammar narrated to us, Simak al-Hanafi narrated to us—Abu Zamil said—Ibn 'Abbas narrated to me, he said: 'Umar ibn al-Khattab narrated to me, he said: When the day of Badr arrived, the Prophet, peace and blessings of Allah be upon him, faced the Qibla, then stretched out his hands, then said: "O Allah, fulfill for me what You have promised me. O Allah, bring me what You have promised me. O Allah, if You destroy this band of the people of Islam, You will never be worshipped on the earth again." He continued to beseech his Lord and supplicate until his cloak fell off. Then Allah, the Almighty and Majestic, revealed: "When you were seeking help of your Lord, and He answered you: 'I will reinforce you with a thousand angels, following one another.'"