Surah Ali 'Imran 3:166

وَمَآ أَصَـٰبَكُمْ يَوْمَ ٱلْتَقَى ٱلْجَمْعَانِ فَبِإِذْنِ ٱللَّهِ وَلِيَعْلَمَ ٱلْمُؤْمِنِينَ

And what struck you on the day the two armies met [at Uḥud] was by permission of Allāh that He might make evident the [true] believers

Translation: Saheeh International

Tafsir

And what afflicted you the day the two hosts encountered at Uhud was by God’s leave by His will and that He might know through knowledge manifested outwardly the true believers.

Excerpt from Tafsir al-Jalalayn, commentary on 3:166, via Quran.com. The reader has the full commentary and 9 more tafsirs.