Ibn Majah

Commentary:
In the hadith, the word "iraqib" is used, which is the plural of "urqub."
By this is meant the back part between both ankles, which is above the heel.
This shows that it is necessary to wash the feet including the ankles, and from the back as well, the feet should be washed up to the same extent.

Benefit:
Ablution (wudu) should be completed fully; not even the smallest part of the limbs of ablution should remain dry, otherwise the ablution will not be valid. If the ablution itself is not valid, then the prayer (salah) will also not be valid. If the prayer is not valid, then a person will go to Hell. The caliph should also keep an eye on the people's ablution to ensure that they are not performing it incorrectly. In our era, we encounter some people who are distant from the religion, and who consider ablution, prayer, and other acts insignificant, and they mock the scholars for this. May Allah guide such people. In ablution, the heels of the feet must also be washed, as they are part of the feet, and wiping (masah) over the feet in ablution is invalid; washing is obligatory (fard). However, wiping (masah) over socks and leather socks (khuffayn) is permissible.