Purity: Assisted Tayammum (When Unable to Perform Alone)
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 700:
If someone’s duty is to perform tayammum but he cannot perform it on his own, he must get help from someone else. The helper must take the mukallaf’s hands and strike them on something with which tayammum can be validly performed; then, the helper must place the mukallaf’s hands on the mukallaf’s forehead and the back of the mukallaf’s hands so that the mukallaf himself wipes the palms of his two hands over his forehead and the back of his hands, if it is possible for him to do so. If it is not possible, the helper must perform tayammum on the mukallaf with the mukallaf’s own hands [i.e. after the helper has placed the mukallaf’s hands on the mukallaf’s forehead and the back of the mukallaf’s hands, the helper must draw the mukallaf’s hands over his forehead and the back of his hands]. If this is not possible, the helper must strike his own hands on something with which tayammum can be validly performed and wipe them over the mukallaf’s forehead and the back of the mukallaf’s hands. In these two cases, based on obligatory precaution, both of them must make the intention of tayammum. However, in the first case [where the mukallaf’s own hands are used], it is sufficient if only the mukallaf makes this intention.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)


