Testing and Trials (Fitna)

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