The Prophet (ﷺ) said: “Cool it down with water,” and he said: “It is from the heat of Hell-fire.”
Sunan Ibn Majah Book 31, Hadith 39
← Previous Hadith “I heard the Prophet (ﷺ) say: ‘Fever is from the heat of the Hell-fire, so cool it down with water.’ He entered upon a son of ‘Ammar and said: ‘Take away the harm, O Lord of mankind, O God of mankind.’”

Sunan Ibn Majah Book 31, Hadith 38 Next Hadith → “Fever is one of the bellows of Hell, so avert it from yourselves with cold water.”

Sunan Ibn Majah Book 31, Hadith 40