Purity: Tayammum with Wounds or Bandages

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 697:

If there is a wound on one’s forehead or the back of his hands, and the cloth or something else that is tied over it cannot be untied, he must wipe his hands over it. If there is a wound on the palms of his hands and the cloth or something else that is tied over it cannot be untied, one must strike his hands on something with which tayammum can be validly performed with the same cloth tied over the wound and wipe over his forehead and the back of his hands. However, if part of the cloth is open, then striking and wiping with that open part is sufficient.

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