Purity: Impurity of the Foot Preventing Wiping

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 259

If the upper part of one’s foot is impure and it cannot be washed [and made pure] so that it can be wiped, then tayammum must be performed.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)