Musannaf Ibn Abi Shayba 36:136

Muhammad ibn Fudayl narrated to us, from Dawud ibn Abi Hind, from Amir, who said: When the day of Badr occurred, the Muslims spoke of Karz ibn Jabir aiding the polytheists, and that weighed heavily upon the Muslims. Then was revealed: "Yes, if you remain patient and conscious of Allah and the enemy come upon you [attacking] in their heat [of rage], your Lord will reinforce you with five thousand angels having marks." He said: "If Karz reinforces them, I will reinforce you with these angels." But Karz did not reinforce them with anything.