Volumn 007, Book 071, Hadith Number 619. 
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Narated By Nazi'

Radi-Allahu 'anhu : Abdullah bin 'Umar

Radi-Allahu 'anhu said, "The Prophet

Sallallahu 'Alaihi Wa 'Aalehi Wa Sallam said, 'Fever is from the heat of Hell, so put it out (cool it) with water.' " Nafi'

Radi-Allahu 'anhu

added: 'Abdullah

Radi-Allahu 'anhu

used to say, "O Allah! Relieve us from the punishment," (when he suffered from fever).

comment: this Hadith suggests that when you have fever, drink a lot of water as fever has a lot of heating effect

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