Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
suyuti:1274a

"When one of you suffers from fever - and indeed fever is a piece of the Fire - let him extinguish it with water. Let him stand in a flowing river facing the direction of it and say: Allahummashfi 'abdaka wa saddik Rasulak ('In the name off Allah. O Allah! Cure your slave and testify to Your Messenger.)' Doing so after Salat As-Subh(Fajr) and before the rising of the sun. Let him submerse himself in it three times, for three days. If he is not cured in three, then five. If he is not cured in five, then seven. If he is not cured in seven, then nine. For indeed it will not remain after nine, with the permission of Allah." (Using translation from Tirmidhī 2084)   

السيوطي:١٢٧٤a

"إِذَا أصاب أحدَكم الحُمَّى، فإن الحمى قطعةٌ من النار" ولفظ طب -من نارِ جهنَّمَ- فليُلطفها عنه بالماءِ- زاد طب: - البارد- فليَستْنقِعْ في نهر جار، وليَستَقْبِلْ جرِيتَهِ يقولُ: بسم اللهِ الرحمنِ الرحيم، اللَّهُمَ اشفِ عبدَك، وصدَق رسولُك، بعدَ

صلاةِ الصبح قبل طلوع الشمسِ، ولينْغَمِسْ فيه ثلاثَ غمَسات ثلاثةَ أيامٍ، فإن لم يبْرأ في ثلاث فخمسٌ، فإن لم يبرأ فسبعٌ، فإنها لا تكادُ تجاوزُ تِسْعًا بإذنِ اللهِ".  

[حم] أحمد [ت] الترمذي حسن غريب، وابن السنى في عمل يوم وليلة، وأبو نعيم في الطب، [طب] الطبرانى في الكبير [ض] ضياء المقدسي في مختاره عن ثوبان

See similar narrations below:

Collected by Tirmidhī, Aḥmad, Ṭabarānī
tirmidhi:2084Aḥmad b. Saʿīd al-Ashqar al-Ribāṭī > Rawḥ b. ʿUbādah > Marzūq Abū ʿAbdullāh al-Shāmī > Saʿīd a man from Ahl al-Shām > Thawbān

"When one of you suffers from fever - and indeed fever is a piece of the Fire - let him extinguish it with water. Let him stand in a flowing river facing the direction of it and say: Allahummashfi 'abdaka wa saddik Rasulak ('In the name off Allah. O Allah! Cure your slave and testify to Your Messenger.)' Doing so after Salat As-Subh(Fajr) and before the rising of the sun. Let him submerse himself in it three times, for three days. If he is not cured in three, then five. If he is not cured in five, then seven. If he is not cured in seven, then nine. For indeed it will not remain after nine, with the permission of Allah."  

Abū ʿĪsá said that this Ḥadīth is Gharīb.
الترمذي:٢٠٨٤حَدَّثَنَا أَحْمَدُ بْنُ سَعِيدٍ الأَشْقَرُ الرِّبَاطِيُّ قال حَدَّثَنَا رَوْحُ بْنُ عُبَادَةَ قال حَدَّثَنَا مَرْزُوقٌ أَبُو عَبْدِ اللَّهِ الشَّامِيُّ قال حَدَّثَنَا سَعِيدٌ رَجُلٌ مِنْ أَهْلِ الشَّامِ أَخْبَرَنَا ثَوْبَانُ

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا أَصَابَ أَحَدَكُمُ الْحُمَّى فَإِنَّ الْحُمَّى قِطْعَةٌ مِنَ النَّارِ فَلْيُطْفِئْهَا عَنْهُ بِالْمَاءِ فَلْيَسْتَنْقِعْ نَهْرًا جَارِيًا لِيَسْتَقْبِلَ جَرْيَةَ الْمَاءِ فَيَقُولُ بِسْمِ اللَّهِ اللَّهُمَّ اشْفِ عَبْدَكَ وَصَدِّقْ رَسُولَكَ بَعْدَ صَلاَةِ الصُّبْحِ قَبْلَ طُلُوعِ الشَّمْسِ فَلْيَغْتَمِسْ فِيهِ ثَلاَثَ غَمَسَاتٍ ثَلاَثَةَ أَيَّامٍ فَإِنْ لَمْ يَبْرَأْ فِي ثَلاَثٍ فَخَمْسٌ وَإِنْ لَمْ يَبْرَأْ فِي خَمْسٍ فَسَبْعٌ فَإِنْ لَمْ يَبْرَأْ فِي سَبْعٍ فَتِسْعٌ فَإِنَّهَا لاَ تَكَادُ تُجَاوِزُ تِسْعًا بِإِذْنِ اللَّهِ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ غَرِيبٌ
ahmad:22425Rawḥ > Marzūq Abū ʿAbdullāh al-Shāmī > Saʿīd a man from Ahl al-Shām > Thawbān

"When one of you suffers from fever - and indeed fever is a piece of the Fire - let him extinguish it with water. Let him stand in a flowing river facing the direction of it and say: Allahummashfi 'abdaka wa saddik Rasulak ('In the name off Allah. O Allah! Cure your slave and testify to Your Messenger.)' Doing so after Salat As-Subh(Fajr) and before the rising of the sun. Let him submerse himself in it three times, for three days. If he is not cured in three, then five. If he is not cured in five, then seven. If he is not cured in seven, then nine. For indeed it will not remain after nine, with the permission of Allah." (Using translation from Tirmidhī 2084)   

أحمد:٢٢٤٢٥حَدَّثَنَا رَوْحٌ حَدَّثَنَا مَرْزُوقٌ أَبُو عَبْدِ اللهِ الشَّامِيُّ حَدَّثَنَا سَعِيدٌ رَجُلٌ مِنْ أَهْلِ الشَّامِ حَدَّثَنَا ثَوْبَانُ

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا أَصَابَ أَحَدَكُمُ الْحُمَّى وَإِنَّ الْحُمَّى قِطْعَةٌ مِنَ النَّارِ فَلْيُطْفِهَا عَنْهُ بِالْمَاءِ الْبَارِدِ وَلْيَسْتَقْبِلْ نَهَرًا جَارِيًا يَسْتَقْبِلُ جِرْيَةَ الْمَاءِ فَيَقُولُ بِاسْمِ اللهِ اللهُمَّ اشْفِ عَبْدَكَ وَصَدِّقْ رَسُولَكَ بَعْدَ صَلَاةِ الْفَجْرِ قَبْلَ طُلُوعِ الشَّمْسِ فَيَغْتَمِسُ فِيهِ ثَلَاثَ غَمَسَاتٍ ثَلَاثَةَ أَيَّامٍ فَإِنْ لَمْ يَبْرَأْ فِي ثَلَاثٍ فَخَمْسٍ فَإِنْ لَمْ يَبْرَأْ فِي خَمْسٍ فَسَبْعٍ فَإِنْ لَمْ يَبْرَأْ فِي سَبْعٍ فَتِسْعٍ؛ فَإِنَّهُ لَا يَكَادُ يُجَاوِزُ التِّسْعَ بِإِذْنِ اللهِ  

tabarani:1450Idrīs b. Jaʿfar al-ʿAṭṭār > Rawḥ b. ʿUbādah > Marzūq Abū ʿAbdullāh al-Shāmī > Saʿīd al-Shāmī > Thawbān

[Machine] The Messenger of Allah ﷺ said, "If any of you is struck with fever, let him extinguish it with cold water, pouring it three times over himself, saying, 'O Allah! Make it cool, beneficial and a means of purification from sins.' For indeed, fever is a part of the heat of Hellfire. So let him extinguish it."  

الطبراني:١٤٥٠حَدَّثَنَا إِدْرِيسُ بْنُ جَعْفَرٍ الْعَطَّارُ ثنا رَوْحُ بْنُ عُبَادَةَ عَنْ مَرْزُوقٍ أَبِي عَبْدِ اللهِ الشَّامِيِّ عَنْ سَعِيدٍ الشَّامِيِّ قَالَ سَمِعْتُ ثَوْبَانَ يَقُولُ

قَالَ رَسُولُ اللهِ ﷺ «إِذَا أَصَابَتْ أَحَدَكُمْ فَإِنَّ الْحُمَّى قِطْعَةٌ مِنْ نَارِ جَهَنَّمَ فَلْيُطْفِئْهَا عَنْهُ بِالْمَاءِ الْبَارِدِ جَارِيًا مُسْتَقْبِلَ جَرْيَةَ الْمَاءِ وَلْيَقُلِ اللهُمَّ صَدِّقْ رَسُولَكَ وَاشْفِ عَبْدَكَ بَعْدَ الْفَجْرِ قَبْلَ طُلُوعِ الشَّمْسِ ولْيَغْمِسْ فِيهِ ثَلَاثَ غَمَسَاتٍ فَإِنْ لَمْ يَبْرَأْ فِي خَمْسٍ فَفِي سَبْعٍ وَإِنْ لَمْ يَبْرَأْ فِي سَبْعٍ فَفِي تِسْعٍ فَإِنَّهَا لَا تَكَادُ أَنْ تُجَاوِزَ التِّسْعَ بِإِذْنِ اللهِ»