Hadith Q190

وَالدَّلِيلُ عَلَى أَنَّ الرُّخْصَةَ فِي الْمَسْحِ عَلَى الْخُفَّيْنِ لِلَابِسِهَا عَلَى طَهَارَةٍ، دُونَ لَابِسِهَا مُحْدِثًا غَيْرَ مُتَطَهِّرٍ‏.‏
And the explanation of the evidence that the concession of wiping over the leather socks is for the person who wore them after performing ablution, and not for the one who wore them without purification, without ablution.
Hadith Reference صحيح ابن خزيمه / جماع أبواب المسح على الخفين / Q190