All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The hands that should be wiped during Tayammum are the hands, both the palms and the upper part of the hand [i.e., the opposite side of the palm], so the two palms are entirely wiped, including rubbing between the fingers, along with wiping the wrist bone.
Al-Sharh Al-Kabeer reads: “He wipes his face with the insides of his fingers [i.e, with the palms], and the back of his hands to the wrist bone with his palms, and it is desirable to rub one of the palms with the other, but it is not obligatory. Because the obligation of wiping the two palms is waived by passing each one on the back of the palm.”
Kashshaf Al-Qinaa’ reads: “(He wipes his hands to the wrist bone), Allah Says (what means): {and hands} [Quran 5:6], if the mentioning of the hand was absolute, then the arms are not included; for example, cutting off the hands of the thief (if the hands are cut off from the wrist bone, not above it, the place of the cut must be wiped) because some of the obligatory areas (for tayammum) remained as if it was cut off less than the wrist bone.” [End of quote]
Allah knows best.