He sweats and sees a trace of najaasah (impurity) on his underwear

No File Exists
Check below answers in case you are looking for other related questions:
He suffers from ongoing emission of madhiy; how can he avoid the najaasah caused by it?
Ruling on the purity of maniy (semen)

No File Exists
Related Answers:
The difference between maniy, madhiy and moisture
It is not permissible to swallow blood coming from the lip or gum because it is naajis (impure)
She is uncertain whether the furnishings in her house are naajis (impure)
He suffers from ongoing emission of madhiy; how can he avoid the najaasah caused by it?
Ruling on the purity of maniy (semen)

Recommended answers for you:
Being Successful in Life
Ruling on hanging verses of the Qur'an on walls
Praying for the newborn to be righteous in various ways
Performing Another ‘Umrah While in Makkah
The believer’s attitude towards calamities