If religion were based on personal opinion, the underside of the leather sock would be more deserving of being wiped than the top. Yet I saw the Messenger of Allah ﷺ wiping over the upper surface of his leather socks.
لو كان الدين بالرأي لكان أسفل الخف أولى بالمسح من أعلاه، وقد رأيت رسول الله ﷺ يمسح على ظاهر خفيه.
Abu Dawud narrated it (162), saying, Muhammad bin Ala told us, Hafs, meaning Ibn Ghiyath, told us, from Amash, from Abu Ishaq, from Abd Khayr, from Ali, and he mentioned it. Its isnad is sahih, and Amash was among the most reliable students of Abu Ishaq. Then Abu Dawud narrated it with another isnad from Amash, and its wording was, "I used not to think the soles of the feet more deserving of washing, until I saw the Messenger of Allah wiping over the top of his socks." In another narration it is likewise the same, both by way of Amash. Then Abu Dawud said, Abu Sawda narrated it, from Ibn Abd Khayr, from his father, who said, I saw Ali perform wudu, and he washed the top of his feet, and he said, "Were it not that I saw the Messenger of Allah do it." And he continued the hadith.For more, see Al-Madkhal ila Sunan al-Kubra by Bayhaqi (219).