Sunan Ibn Majah, Book 31, Hadith 3601 (In-Book) ⓘ
It was narrated from Ibn ‘Umar that the Prophet said: “Intense fever is from the heat of Hell-fire, so cool it down with water.”
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عُمَرَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ أَنَّهُ قَالَ " إِنَّ شِدَّةَ الْحُمَّى مِنْ فَيْحِ جَهَنَّمَ فَابْرُدُوهَا بِالْمَاءِ " .
also referenced under: Hadith 3472 (Reference) & Volume 4, Book 31, Hadith 3472 (DarusSalam)