Ibn Shawdhab said: On the day of Badr, the father of Abu Ubaydah kept confronting Abu Ubaydah, while Abu Ubaydah kept avoiding him. When he did this repeatedly, Abu Ubaydah went for him and killed him. So Allah, the Mighty and Majestic, revealed this verse concerning it, when he had killed his father: "You will not find a people who believe in Allah and the Last Day" [al-Mujadilah: 22] to the end of the verse.
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 357