Jami` at-Tirmidhi 2073

(25) – باب مَا جَاءَ فِي تَبْرِيدِ الْحُمَّى بِالْمَاءِ

(25) – What Has Been Related About Cooling Fever with Water

"Rafi' bin Khadij narrated that the Prophet ﷺ said:

"Fever is from the agitation of the Fire, so cool it with water."

Sahih (Authentic)