مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2634
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
Abu Jamrah told us. I was pushing people back from Ibn 'Abbas (رضي الله عنه), then I stayed away for a few days and he said: What kept you away? I said: Fever. He said: The Messenger of Allah (ﷺ) said: "Fever is from the exhalation of Hell, so cool it down with Zamzam water.”
Musnad Ahmad 2649lts isnad is saheeh, al-Bukhari (3261)]