I came to 'A'isha, the wife of the Prophet (ﷺ), on the day when Sa'db. Abi Waqqas died. 'Abd al-Rahman b. Abu Bakr also came there and he performed ablution in her presence. She (Hadrat 'A'isha) said: Abd al-Rahman, complete the ablution as I heard the Allah's Messenger (ﷺ) say: Woe to the heels because of hell-fire.
The Book of Purification - Sahih Muslim 240a
This narration from the Mother of the Believers 'A'isha (may Allah be pleased with her) demonstrates the meticulous attention to detail required in performing ablution (wudu'). The Prophet's warning "Woe to the heels because of hell-fire" serves as a stern admonition against neglecting any part of the limbs that must be washed during purification.
Scholarly Commentary
The context reveals that 'Abd al-Rahman ibn Abi Bakr (may Allah be pleased with him) was performing ablution but apparently did not thoroughly wash his heels. 'A'isha (may Allah be pleased with her) immediately corrected him based on what she heard from the Messenger of Allah (peace be upon him).
This hadith emphasizes the obligation of complete washing of all prescribed body parts in wudu', particularly the heels which are often neglected. The severe warning indicates the gravity of omitting any obligatory part of ablution, as incomplete purification invalidates prayer and other acts of worship.
Scholars derive from this that Muslims must ensure water reaches all parts of the feet during wudu', including between toes and the heels. The prophetic warning serves as both guidance and deterrent, ensuring the ummah maintains the proper standards of ritual purity essential for valid worship.