Sahih al-Bukhari, Volume 4, Book 54, Hadith 486 (USC-MSA) ⓘ
Narrated Ibn `Umar: The Prophet said, "Fever is from the heat of the (Hell) Fire; so abate fever with water."
حَدَّثَنَا مُسَدَّدٌ، عَنْ يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، قَالَ حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْحُمَّى مِنْ فَيْحِ جَهَنَّمَ فَأَبْرِدُوهَا بِالْمَاءِ " .
also referenced under: Book 59, Hadith 74 (In-Book) & Hadith 3264 (DarusSalam)