كتاب السلام
39  
The Book of Greetings
(26)
Chapter: For Every Disease There Is A Remedy, And It Is Recommended To Treat Disease
(26)
باب لِكُلِّ دَاءٍ دَوَاءٌ وَاسْتِحْبَابُ التَّدَاوِي ‏‏
Sahih Muslim 2211 a

Asma' reported that a woman running high fever was brought to her. She asked water to be brought and then sprinkled it in the opening of a shirt at the uppermost part of the chest and said that Allah's Messenger (ﷺ) had said:

Cool (the fever) with water. for it is because of the vehemence of the beat of Hell.
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدَةُ بْنُ سُلَيْمَانَ، عَنْ هِشَامٍ، عَنْ فَاطِمَةَ، عَنْ أَسْمَاءَ، أَنَّهَا كَانَتْ تُؤْتَى بِالْمَرْأَةِ الْمَوْعُوكَةِ فَتَدْعُو بِالْمَاءِ فَتَصُبُّهُ فِي جَيْبِهَا وَتَقُولُ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ ابْرُدُوهَا بِالْمَاءِ ‏"‏ ‏.‏ وَقَالَ ‏"‏ إِنَّهَا مِنْ فَيْحِ جَهَنَّمَ ‏"‏ ‏.‏
Reference : Sahih Muslim 2211a
In-book reference : Book 39, Hadith 111
USC-MSA web (English) reference : Book 26, Hadith 5482
  (deprecated numbering scheme)