Short answer
No. Sweat is pure and does not break wudu in any of the four schools, however much you sweat. The same goes for burping, tears, spit and a runny nose.
Sweat does not break wudu and is pure. Burping, yawning, tears, saliva and nasal mucus also do not break wudu.
The four schools agree on this.
Explanation
The four schools agree that sweat does not break wudu (ablution). Sweat is pure: the sweat of a Muslim, and of any person, is not impure, so it does not make your body or clothes impure either. When Abu Hurayrah avoided sitting with the Prophet ﷺ because he was in a state of janabah, he was told that a believer does not become impure.
So you can make wudu, go to the gym or work outside in the heat, and pray in the same clothes. If they smell strongly of sweat, change them or freshen up before going to the masjid, out of respect for the people beside you.
Other things that do not break wudu:
- Burping: air from the stomach through the mouth is not wind from the back passage.
- Tears, spit and mucus: all pure and do not break wudu.
- Yawning and sneezing: do not break wudu.
- Cutting nails or hair: does not break wudu, and you do not need to wipe the place again.
What does break wudu is listed in what breaks wudu. Ghusl after heavy sweating is not required, though a shower before Jumuah is sunnah.
The evidence
Sahih al-Bukhari 283
Sahih... سبحان الله ان المؤمن لا ينجس ...
"Glory be to Allah, the believer does not become impure."
The body of a believer, and so his sweat, is pure.
Where the ruling is recorded
- al-Fatawa al-Hindiyya, Kitab al-Taharah, chapter on impurities. The sweat of a human is pure.
- Nur al-Idah with Maraqi al-Falah, Chapter on what does not break wudu. Lists things that do not break wudu.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.