وَفَرْضُ ذَلِكَ مِقْدَارُ ثَلَاثِ أَصَابِعَ مِنْ أَصَابِعِ الْيَدِ.
Meaning: The minimum obligatory amount of wiping is the area corresponding to three fingers of the hand.
The three-finger measure applies to the area wiped on the upper surface of each khuff and is measured against fingers of the hand.
The minimal obligatory area is distinct from the preferred technique of drawing finger-lines. The later tear-size rule measures against toes, not fingers of the hand.