Abu Hurayrah, ʿAbd Allah ibn ʿAmr, and ʿAishah—all of them said that the Messenger of Allah ﷺ saw a man performing wudu and leaving a spot the size of a fingernail on his foot unwashed. The Prophet ﷺ noticed it and declared, “Woe to the heels from the Fire!”

Vocabulary of the ḥadith
– “His foot” (qadamah): The word is feminine in Arabic and denotes the part of a person’s leg that treads the ground; above it is the shin, and between the two is the ankle joint.
– “Fingernail” (ẓufr): The preferred pronunciation places a ḍamma on both the ẓāʾ and the fāʾ; its plural is aẓfār. It is the nearly transparent plate found on the upper surface of the last phalanx of the fingers and toes.
– “The water did not reach it” (lam yuṣibhu al-māʾ): The verb aṣāba literally means “to hit the target”; here it means that the water missed that spot and never reached it.
– “Perfect your wudu” (aḥsin wuḍūʾak): Aḥsin means “do the deed well,” that is, complete and perfect your ablution.

Points derived from the ḥadith

1. Every limb included in wudu must be washed in its entirety; if even a small part is left dry, the wudu is invalid.
2. It is recommended to perform wudu well—that is, thoroughly and completely. The text mentions the foot explicitly, and the same ruling applies to the other limbs by analogy.
3. The feet are among the limbs of wudu; merely wiping over them is insufficient—they must be washed, as stated plainly in Qur’an 5:6.
4. Continuity (muwālāt) between the limbs is obligatory. The Prophet ﷺ ordered the man to redo his entire wudu because he had delayed washing his foot after the other limbs; had continuity not been required, he would have told him to wash only the neglected part.
5. Water itself is indispensable for wudu; nothing else can take its place.
6. One must hasten to enjoin what is right and guide the ignorant or heedless so that their acts of worship are performed correctly.