Ruling 683:
The thing with which one performs tayammum must not be usurped; therefore, if one performs tayammum with usurped soil, his tayammum is invalid.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)
Purity: Usurped Materials in Tayammum
Practical Laws of Islam as per the teachings of Ayatullah Sistani
