Sayyidah Khawlah (may Allah be pleased with her) said: I went in to the Prophet (peace and blessings be upon him); he (peace and blessings be upon him) had a fever and the fever had become severe. I said: O Messenger of Allah, your fever has become severe; if only you would supplicate to Allah to remove it from you. He (peace and blessings be upon him) said: "The people most severely tested are the prophets, then those who come after them." She said: A water-skin had been hung for him (peace and blessings be upon him) on a tree and he (peace and blessings be upon him) was lying beneath it, and the water was dripping onto his (peace and blessings be upon him) heart.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20996