Musnad Abu Ya'la al-Mawsili 109:320

Ibn Numayr narrated to us, Ya‘la narrated to us, al-A‘mash narrated to us, from Abu Sufyan, from Jabir, who said: The Prophet, peace and blessings of Allah be upon him, was approached, and it was said to him: "Fever has persisted upon us." He said: "If you wish, it can be lifted from you, and if you wish, it can be a purification for you." They said: "Let it be a purification for us."