Musnad Ahmad 25:790

'Affan narrated to us, Hammam narrated to us, Abu Jamra informed us, he said: I used to push the people away from Ibn 'Abbas, then I was detained for some days. He said: "What detained you?" I said: "The fever." He said: "Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) said: 'Indeed, the fever is from the scorching heat of Hell, so cool it with Zamzam water.'"