Muwatta Malik 1727
موطأ مالك#1727Sahihوَحَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الْحُمَّى مِنْ فَيْحِ جَهَنَّمَ فَأَطْفِئُوهَا بِالْمَاءِ " .
Malik related to me from Nafi from Ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "Fever is from the vehemence of the heat of Jahannam, so put it out with water
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Salim al-HilaliSahih
In-book reference: 50:17