Ali 'Imran 3:166

Wama asabakum yawma iltaqaaljamAAani fabi-ithni Allahi waliyaAAlamaalmu/mineen

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

Whatever you suffered on the day when the two troops faced each other was by the will of Allah, and in order to know the believers,