الْمَسْحُ عَلَى الْخُفَّيْنِ جَائِزٌ بِالسُّنَّةِ مِنْ كُلِّ حَدَثٍ مُوجِبٍ لِلْوُضُوءِ، إِذَا لَبِسَ الْخُفَّيْنِ عَلَى طَهَارَةٍ، ثُمَّ أَحْدَثَ.
Meaning: Wiping over khuffs is permitted by the Sunnah for every state of minor ritual impurity requiring wudu, provided the khuffs were put on in a state of purity and minor impurity occurred afterwards.
The permission concerns minor impurity that calls for wudu. The khuffs are worn while the person has complete wudu, then a later minor impurity occurs. In a later wudu, wiping may replace washing the feet.
If the necessary state of purity was absent when the footwear was put on, the specified condition is not fulfilled.