I heard the Prophet ﷺ say, "Fever comes from the intense heat of Hellfire, so cool it down with water."
سمعت النبي ﷺ يقول: الحمى من فوح جهنم فأبردوها بالماء.
Bukhari narrated it in "Medicine" (5726), and Muslim in "Greetings" (2212:83), both through the route of Abu Ahwas, from Saeed bin Masruq, from Abaya bin Rifa, from his grandfather Rafi bin Khadij, and he related it.Ibn Majah (3473) narrated it through another route, from Musab bin Miqdam, who said, Israil narrated to us, from Saeed bin Masruq, with his chain, and he added to it, "He then visited a child of Ammar's and said, 'Remove the affliction, Lord of mankind, God of mankind.'"Musab bin Miqdam has no harm in him, and he was among the devout worshippers, so perhaps one hadith became mixed into another for him.