Sahih al-Bukhari 3264
Sahih al-Bukhari · Book 59: Beginning of Creation · The description of the (Hell) Fire and the fact that it has already been created
Narrated Ibn `Umar:
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 " .
The Prophet (ﷺ) said, "Fever is from the heat of the (Hell) Fire; so abate fever with water."