Mishkat al-Masabih #1502

Thauban reported God’s messenger as saying, "When one of you has an attack of fever the fever is a portion of hell, so he should quench it with water, bathing in a flowing stream facing the direction of the current and saying, ‘In the name of God. O God, heal Thy servant and varify Thy messenger’ after the morning prayer before sunrise. He should dip himself in it three times a day for three days, and if he is not cured in three days, then for five days, and if he is not cured in five days, then for seven, and if he is not cured in seven days, then for nine, for it will hardly last more than nine days by the permission of God who is great and glorious.” Tirmidhi transmitted it, saying this is a gharib tradition.