Answered by Shaykh Yusuf Weltch
Question
If there is dry najasa on my body (for example, one drop or more on my leg), does it transfer by sweating?
Answer
Kindly consider the explanation below:
Dry Impurities
If one has dry impurity on their body, they sweat; the impurity does not spread. This ruling prevents undue hardship for those not performing istinja’ with water. [Shurunbulali, Maraqi al-Falah]
However, it would be cautious (not obligatory) to wash if the traces of the impurity reappear noticeably.
Hope this helps
Allah A’lam
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani