Purity: Ruling on Mud or Soap Remaining on Clothing After Washing
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 163
If after washing clothing or something similar some mud or soap is seen on it, in the event that one does not deem it probable for it to have prevented the water from reaching the clothing, the clothing is pure. However, if impure water reaches the inside of the mud or soap, the outside of the mud or soap is pure and the inside is impure.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)