It is narrated from Imam Ibrahim al-Nakha'i, may Allah have mercy on him, regarding a person in a state of major ritual impurity (janabah), that if his sweat gets on his clothes, he said: There is no harm, and there is no need to sprinkle water on it.
Hadith Referenceسنن دارمي / من كتاب الطهارة / 1064