Musnad Ahmad 1167:15

Ibn Numayr narrated to us, from Hisham, from Fatimah bint al-Mundhir, from Asma, that when a woman was brought to her for her to supplicate for her, she would pour water between her and her garment (collar), and she said: "Indeed, the Messenger of Allah (ﷺ) commanded us to cool it (the fever) with water, and he said: 'It is from the heat of Hell.'"