Purity: Usurped Materials in Tayammum

Practical Laws of Islam as per the teachings of Ayatullah Sistani

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)