Muwatta Malik
Book 50, Hadith 16
Arabic hadith text
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِنَّ الْحُمَّى مِنْ فَيْحِ جَهَنَّمَ فَابْرُدُوهَا بِالْمَاءِ " .
Translation
Yahya related to me from Malik from Hisham ibn Urwa from hisfather that the Messenger of Allah, may Allah bless him and grant himpeace, said, "Fever is from the vehemence of the heat of Jahannam, socool it with water."