From Sahih Bukhari (Hadith 3261):
Narrated Abu Jamra Ad-Dabi:I used to sit with Ibn `Abbas in Mecca. Once I had a fever and he said (to me), "Cool your fever with Zamzam water, for Allah's Messenger (ﷺ) said: 'It, (the Fever) is from the heat of the (Hell) Fire; so, cool it with water (or Zamzam water)
Reference: Bukhari 3261