Sura 3 Ali 'Imran (Family of Imran), aya 166

1. وَمَا أَصَابَكُمْ يَوْمَ الْتَقَى الْجَمْعَانِ فَبِإِذْنِ اللَّهِ وَلِيَعْلَمَ الْمُؤْمِنِينَ

   And what struck you on the day the two armies met was by permission of Allah that He might make evident the (true) believers.

   3:166

Tafsiri: Saheeh International