Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 619
Narrated Nazi':
Abdullah bin 'Umar said, "The Prophet said, 'Fever is from the heat of Hell, so put it out (cool it) with water.' " Nafi' added: 'Abdullah used to say, "O Allah! Relieve us from the punishment," (when he suffered from fever).