It is narrated from Ikrimah (may Allah have mercy on him) that Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) was asked: If a menstruating woman sweats in her shift during the days of her menstruation, may she pray in that shift? Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: Yes, as long as there is no blood on it. Likewise a man in a state of major impurity (junub) who sweats in his clothes may pray in those same clothes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4123