Hadith Q166

وَالدَّلِيلُ عَلَى أَنَّ الْمَاسِحَ لِلْقَدَمَيْنِ التَّارِكَ لِغَسْلِهِمَا مُسْتَوْجِبٌ لِلْعِقَابِ بِالنَّارِ، إِلَّا أَنْ يَعْفُوَ اللَّهُ وَيَصْفَحَ- نَعُوذُ بِاللَّهِ مِنْ عِقَابِهِ-‏.‏
And the explanation of the evidence that the one who wipes over the feet instead of washing them is deserving of the punishment of the Fire, except if Allah the Exalted forgives and pardons. We seek refuge with Allah the Exalted from His punishment.
Hadith Reference صحيح ابن خزيمه / جماع أبواب الوضوء وسننه / Q166