Sunan At-Tirmidhi

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