Woe to the backsides from the Fire. What does this mean?

The aforementioned Hadith is narrated in the Two Sahihs from Abdullah ibn Amr with the wording: "Woe to the heels from the Fire; perfect your ablution." "Woe" refers to sorrow, destruction, and the hardship of torment. The meaning intended is: Woe to the owners of heels who are negligent in washing them.

The Hadith indicates the obligation of washing the entire feet when they are uncovered. However, if one is wearing khuff (leather socks) that were put on while in a state of ritual purity, then wiping over them is sufficient.