The verse "And whoever turns his back to them on such a day" [Anfal 8:16] was revealed concerning the day of Badr.
حدثنا محمد بن هشام المصري حدثنا بشر بن المفضل حدثنا داود عن أبي نضرة
نزلت في يوم بدر {ومن يولهم يومئذ دبره}
[Its isnad is sahih] Nasai narrated it in Sunan al-Kubra, no. 11204, from the hadith of Bishr bin Mufaddal, through this route. Al-Hakim graded it sahih according to the criteria of Muslim, 2/327, and Dhahabi agreed with him.