I say, and with God's success: If someone has one of his legs cut off below the ankle, then it is considered: if there remains from the back of the foot a length of three fingers from the smallest fingers of the hand or more, he is allowed to wipe over his socks; otherwise, he must wash them and not wipe, because it is a condition for the permissibility of wiping that there remains on each foot from the front of the foot in the sock the length of three fingers from the smallest fingers of the hand; this is to ensure the required amount for the place of wiping, just as washing the place of the cut is obligatory, and it is not permissible to combine washing and wiping. See: Nihayat al-Mirad, p. 380, and God knows best.