The Prophet ﷺ said, "Fever comes from the intense heat of Hellfire, so cool it down with water."
حدثنا يحيى عن عبيد الله حدثني نافع
عن النبي ﷺ الحمى من فيح جهنم فأبردوها بالماء
Its isnad is sahih. Bukhari related it in 10:147 through the route of Ibn Wahb, from Malik, from Nafi. Hafiz said in Fath al-Bari, "Muslim related it likewise, and Nasai related it through the route of Abdul-Rahman bin Qasim, from Malik."Daraqutni said in Muwattat, "None of Malik's companions related it in Muwatta except Ibn Wahb and Ibn Qasim, and Shafii, Saeed bin Afir, and Saeed bin Dawud followed them in this, but Ibn Maen did not bring it, nor did Qanabi, nor Abu Musab, nor Ibn Bukayr." End of quote. Ibn Abdul-Barr said the same in Taqassi.Ibn Majah related it in 2:182 through the route of Ibn Numayr, from Ubaydullah bin Umar, from Nafi. Something similar in meaning has already passed from the hadith of Ibn Abbas, number 2649.