ثُمَّ فَاءُوا مِنْهُمْ بِقَاصِمَةِ الظَّهْرِ وَلَا يَبْرُدُ الْغَلِيلَ الْمَاءُ
Translation: Then they returned with a back-breaking blow from them, and even water could not cool the burning anguish.
Fāʾū means “they returned.” Qāṣimat al-ẓahr is a blow that breaks the back, a metaphor for devastating defeat. Ghalīl expresses burning inner anguish or thirst for redress, and lā yabrudu ... al-māʾ makes ordinary water incapable of cooling it.
The coupled images of a broken back and unquenched burning intensify the psychological and collective cost of conflict, not a literal medical description.