Fever is from the heat of the Hell-Fire so cool it down with water Sunan Ibn Majah 3474
Arabic hadith text
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدَةُ بْنُ سُلَيْمَانَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ فَاطِمَةَ بِنْتِ الْمُنْذِرِ، عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ، أَنَّهَا كَانَتْ تُؤْتَى بِالْمَرْأَةِ الْمَوْعُوكَةِ فَتَدْعُو بِالْمَاءِ فَتَصُبُّهُ فِي جَيْبِهَا وَتَقُولُ إِنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ قَالَ " ابْرُدُوهَا بِالْمَاءِ " . وَقَالَ " إِنَّهَا مِنْ فَيْحِ جَهَنَّمَ "
Translation
It wasnarrated from Asma’ bint Abu Bakr that a woman suffering fromfeverwould be brought to her, and she would call for water and pouritonto the neck of her garment. She said
The Prophet (ﷺ) said:“Coolit down with water,” and he said: “It is from the heat ofHell-fire.”