Musannaf Ibn Abi Shayba 36:164

Ubayd Allah narrated to us, he said: Isra'il informed us, from Abu Ishaq, from Abu Ubaydah, from his father, who said: They were made to appear few in our eyes on the day of Badr, until I said to a companion of mine beside me, "How many do you see them?" He said, "I see them as a hundred." Until we captured a man from them and asked him, and he said, "We were a thousand."