What is the meaning of 'al-Ka'bain' (the two ankles) in relation to washing the feet?
Chapter on the Obligation of Purification
Al-Mughni
Book of Purification
Primary text
The commonly understood meaning of al-Ka'bain (the ankles) refers to the prominent bones at the lower part of the leg where it joins the foot. This interpretation is supported by the customary usage among Arabs and by narrations describing standing in prayer where the ankles of one person were touching the ankles of another. The Quranic reference uses the dual form ('al-Ka'bain'), which indicates that this boundary applies to each individual foot, consistent with washing up to that point on both.
Supporting text
A dissenting view, attributed to Muhammad ibn al-Hasan, suggests that al-Ka'bain refers to the prominence on the upper part of the foot where the sandal strap fastens (mashat al-qadam). This interpretation is rejected because if the intent was to include all prominent ankle bones, the plural form ('al-Kaba'ib') would have been used, similar to how the limit for the hands was specified as 'al-Marāfiq' (elbows).