It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you has a fever, let him pour cold water over himself at the time of sahar (before dawn) for three nights." This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs (Bukhari and Muslim) did not record it. And its supporting hadith (shahid) is the following:

It is narrated from a maidservant of Sayyiduna al-Zubayr (may Allah be pleased with him) that she said: Whenever al-Zubayr (may Allah be pleased with him) had a fever, the Prophet (peace and blessings be upon him) would order us to cool water and then pour it over him.

It is narrated from Abu Jamrah that he said: I used to push people back (because of the crowd) from around Sayyiduna Ibn Abbas (may Allah be pleased with them both). Then I stayed away from his gathering for a few days. He asked: "What kept you away?" I said: "Fever." So he said that the Messenger of Allah (peace and blessings be upon him) said: "Fever is from the intense heat of Hell, so cool it with water." This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it with this addition.

It is narrated from Sayyiduna Samurah bin Jundub (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Indeed, fever is a piece of the Fire, so cool it away from yourselves with water." The narrator said: And when the Messenger of Allah (peace and blessings be upon him) had a fever, he would call for a waterskin of water, pour it over his head and take a bath. This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it with this addition.