Narrated 'Atiyyah:
Abu Sa'eed narrated: "On the Day of Badr, the Romans had a victory over the Persians. So the believers were pleased with that, then the following was revealed: 'Alif Lam Mim. The Romans have been defeated, up to His saying: 'the believers will rejoice - with the help of Allah... (30:1-5)'" He said: "So the believers were happy with the victory of the Romans over the Persians." (DE)
English reference (DE): Vol. 5, Book 44, Hadith 3192 (DE)
Arabic reference (DE): Book 47, Hadith 3496 (DE)