Musnad Ahmad 1153:585

Sulayman ibn Dawud al-Hashimi narrated to us, he said: Ibrahim ibn Sa’d informed us, from Hisham ibn ‘Urwah, from his father, from ‘Aishah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, fever is from the scorching heat of Hell, so cool it with water." Ibrahim said: "I did not hear anything from Hisham except this one single hadith."