Ibn 'Abbas narrated:
For fever, and all pains, the Prophet (S.A.W) would teach them to say: Bismillahil-Kabir; a'udhu billahil-'Azimi min sharri kulli 'irqin na'arin, wa min sharri harrin-nar. (In the name of Allah the great, I seek refuge with Allah he magnificent of the evil of every gushing vein, and from the evil of the heat of the Fire)