Ar-Rum 30:8

وَيَوْمَئِذٍ يَفْرَحُ الْمُؤْمِنُونَ - بِنَصْرِ اللَّهِ ۚ

(And on that day, the believers will rejoice – with the help of Allah.) They will rejoice because the Romans, the companions of Caesar, the king of Ash-Sham, defeated the Persians, the companions of Chosroes, who were Zoroastrians. According to many of the scholars, such as Ibn Abbas, Ath-Thawri, As-Suddi and others, the victory of the Romans over the Persians happened on the same day as the battle of Badr. It was reported in the Hadith recorded by At-Tirmidhi, Ibn Jarir, Ibn Abi Hatim and Al-Bazaar that Abu Said said: “On the day of Badr, the Romans defeated the Persians, and the believers were happy and rejoiced about that. And Allah revealed the words:

وَيَوْمَئِذٍ يَفْرَحُ الْمُؤْمِنُونَ -ِنَصْرِ اللَّهِ ۚ يَنصُرُ مَن يَشَاءُ ۖ وَهُوَ الْعَزِيزُ الرَّحِيمُ

(And on that day, the believers will rejoice – with the help of Allah. He helps whom He wills, and He is the All-Mighty, the Most Merciful.) Ibn Abi Htim recorded that Az-Zubayr Al-Kilabi said, I saw the victory of the Persians over the Romans, then I saw the victory of the Romans over the Persians, then I saw the victory of the Muslims over both the Persian and Romans, and all of that happened within fifteen years.” Allah’s saying: