Surah Ar-Rum 30:5

بِنَصْرِ ٱللَّهِ ۚ يَنصُرُ مَن يَشَآءُ ۖ وَهُوَ ٱلْعَزِيزُ ٱلرَّحِيمُ

In the victory of Allāh. He gives victory to whom He wills, and He is the Exalted in Might, the Merciful.

Translation: Saheeh International

Tafsir

in God’s help to them against the Persians. They the believers indeed rejoiced in this as they came to know of it on the day that it took place on the day of the battle of Badr when Gabriel came down with this news thereon in addition to their rejoicing in their victory over the idolaters on that same day. …

Excerpt from Tafsir al-Jalalayn, commentary on 30:5, via Quran.com. The reader has the full commentary and 9 more tafsirs.