لَا يُقَـٰتِلُونَكُمْ جَمِيعًا إِلَّا فِى قُرًۭى مُّحَصَّنَةٍ أَوْ مِن وَرَآءِ جُدُرٍۭ ۚ بَأْسُهُم بَيْنَهُمْ شَدِيدٌۭ ۚ تَحْسَبُهُمْ جَمِيعًۭا وَقُلُوبُهُمْ شَتَّىٰ ۚ ذَٰلِكَ بِأَنَّهُمْ قَوْمٌۭ لَّا يَعْقِلُونَ
“You think they are one group, but in reality, their hearts are disunited.”
Applied to the disunity within the Quraysh ranks as they marched out to Badr.
This ayah is part of Surah al-Hashr, which -- as this event's own significance note states -- was revealed about the expulsion of Banu Nadir (Ibn Abbas RA preferred to call it Surat Banu Nadir).