Answered by Shaykh Yusuf Weltch
If there is dry najasa on my body (for example, one drop or more on my leg), does it transfer by sweating?
Kindly consider the explanation below:
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
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani
Shaykh Yusuf Weltch is a teacher of Arabic, Islamic law, and spirituality. After accepting Islam in 2008, he then completed four years at the Darul Uloom seminary in New York where he studied Arabic and the traditional sciences. He then traveled to Tarim, Yemen, where he stayed for three years studying in Dar Al-Mustafa under some of the greatest scholars of our time, including Habib Umar Bin Hafiz, Habib Kadhim al-Saqqaf, and Shaykh Umar al-Khatib. In Tarim, Shaykh Yusuf completed the memorization of the Qur’an and studied beliefs, legal methodology, hadith methodology, Qur’anic exegesis, Islamic history, and a number of texts on spirituality. He joined the SeekersGuidance faculty in the summer of 2019.