Distress from Satan
Remember when you fled without looking back, while the Messenger called to you from behind? Allah repaid you with distress upon distress so that you would not grieve over what you lost or what befell you.
3:153When ye climbed (the hill) and paid no heed to anyone, while the messenger, in your rear, was calling you (to fight). Therefor He rewarded you grief for (his) grief, that (He might teach) you not to sorrow either for that which ye missed or for that which befell you. Allah is Informed of what ye do.