We mentioned the Hadiths by the two Leaders of the Faithful, `Uthman and `Ali, and also by Ibn `Abbas, Mu`awiyah, `Abdullah bin Zayd bin `Asim and Al-Miqdad bin Ma`dikarib, that the Messenger of Allah washed his feet for Wudu', either once, twice or thrice. It is recorded in the Two Sahihs that `Abdullah bin `Amr said, "The Messenger of Allah was once late during a trip we were taking, and he caught up with us when the time remaining for the `Asr prayer was short. We were still performing Wudu' (in a rush) and we were wiping our feet. He shouted at the top of his voice,
«أَسْبِغُوا الْوُضُوءَ وَيْلٌ لِلْأَعْقَابِ مِنَ النَّار»
(Perform Wudu' thoroughly. Save your heels from the Fire.)'' The same narration was also collected in the Two Sahihs from Abu Hurayrah. Muslim recorded that `A'ishah said that the Prophet said,
«أَسْبِغُوا الْوُضُوءَ وَيْلٌ لِلْأَعْقَابِ مِنَ النَّار»
(Perform Wudu' thoroughly. Save your heels from the Fire.) `Abdullah bin Al-Harith bin Jaz' said that he heard the Messenger of Allah saying,
«وَيْلٌ لِلْأَعْقَابِ وَبُطُونِ الْأَقْدَامِ مِنَ النَّار»
(Save your heels and the bottom of the feet from the Fire. ) It was recorded by Al-Bayhaqi and Al-Hakim, and this chain is Sahih. Muslim recorded that `Umar bin Al-Khattab said that a man once performed Wudu' and left a dry spot the size of a fingernail on his foot. The Prophet saw that and he said to him,
«ارْجِعْ فَأَحْسِنْ وُضُوءَك»
(Go back and perform proper Wudu'.) Al-Hafiz Abu Bakr Al-Bayhaqi also recorded that Anas bin Malik said that a man came to the Prophet , after he performed Wudu' and left a dry spot the size of a fingernail on his foot. The Messenger of Allah said to him,
«ارْجِعْ فَأَحْسِنْ وُضُوءَك»
(Go back and perform proper Wudu'.) Imam Ahmad recorded that some of the wives of the Prophet said that the Prophet saw a man praying, but noticed a dry spot on his foot, the size of a Dirham. The Messenger of Allah ordered that man to perform Wudu' again. This Hadith was also collected by Abu Dawud from Baqiyyah, who added in his narration, "And (the Prophet ordered him) to repeat the prayer.'' This Hadith has a strong, reasonably good chain of narrators. Allah knows best.