The face is one area, while the two arms and two feet are physically four more limbs. Yet the text says “three limbs.”
The counting is by legal categories: face, arms, and feet.
Thus the expression describes three kinds of washing and does not conflict with the four total obligations of wudu.
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Why the Text Says Three Limbs
Taharah and Wudu Obligations: Limits, Evidence and Juristic Differences
The face is one area, while the two arms and two feet are physically four more limbs. Yet the text says “three limbs.”
The counting is by legal categories: face, arms, and feet.
Thus the expression describes three kinds of washing and does not conflict with the four total obligations of wudu.