The Messenger of Allah ﷺ wiped over the socks. Another version adds: "On the back (upper part) of the socks."  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يَمْسَحُ عَلَى الْخُفَّيْنِ وَقَالَ غَيْرُ مُحَمَّدٍ عَلَى ظَهْرِ الْخُفَّيْنِ  

If the religion were based on opinion, it would be more important to wipe the under part of the shoe than the upper but I have seen the Messenger of Allah ﷺ wiping over the upper part of his shoes.  

لَوْ كَانَ الدِّينُ بِالرَّأْىِ لَكَانَ أَسْفَلُ الْخُفِّ أَوْلَى بِالْمَسْحِ مِنْ أَعْلاَهُ وَقَدْ رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَمْسَحُ عَلَى ظَاهِرِ خُفَّيْهِ  

“I always preferred to wash the under part of the feet until I saw the Messenger of Allah ﷺ wiping the upper part of them.  

مَا كُنْتُ أُرَى بَاطِنَ الْقَدَمَيْنِ إِلاَّ أَحَقَّ بِالْغَسْلِ حَتَّى رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَمْسَحُ عَلَى ظَهْرِ خُفَّيْهِ  

If religion were based on opinion, it would be more proper to wipe the under part of the feet than the upper. The Prophet ﷺ wiped over the upper part of his shoes. The narrator Waki’ said: I saw ‘ Ali perform ablution and wash the upper part of his feet, and say : Had I not seen the Messenger of Allah ﷺ doing like this –and he narrated the tradition in full.  

لَوْ كَانَ الدِّينُ بِالرَّأْىِ لَكَانَ بَاطِنُ الْقَدَمَيْنِ أَحَقَّ بِالْمَسْحِ مِنْ ظَاهِرِهِمَا وَقَدْ مَسَحَ النَّبِيُّ ﷺ عَلَى ظَهْرِ خُفَّيْهِ وَرَوَاهُ وَكِيعٌ عَنِ الأَعْمَشِ بِإِسْنَادِهِ قَالَ كُنْتُ أُرَى أَنَّ بَاطِنَ الْقَدَمَيْنِ أَحَقُّ بِالْمَسْحِ مِنْ ظَاهِرِهِمَا حَتَّى رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَمْسَحُ عَلَى ظَاهِرِهِمَا قَالَ وَكِيعٌ يَعْنِي الْخُفَّيْنِ وَرَوَاهُ عِيسَى بْنُ يُونُسَ عَنِ الأَعْمَشِ كَمَا رَوَاهُ وَكِيعٌ وَرَوَاهُ أَبُو السَّوْدَاءِ عَنِ ابْنِ عَبْدِ خَيْرٍ عَنْ أَبِيهِ قَالَ رَأَيْتُ عَلِيًّا تَوَضَّأَ فَغَسَلَ ظَاهِرَ قَدَمَيْهِ وَقَالَ لَوْلاَ أَنِّي رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَفْعَلُهُ وَسَاقَ الْحَدِيثَ  

I poured water while the Prophet ﷺ performed ablution in the battle of Tabuk. He wiped over the upper part of the socks and their lower part. Abu Dawud said: I have been told that Thawr did not hear this tradition from Raja'.  

وَضَّأْتُ النَّبِيَّ ﷺ فِي غَزْوَةِ تَبُوكَ فَمَسَحَ أَعْلَى الْخُفَّيْنِ وَأَسْفَلَهُمَا