Hadith: I saw the Messenger of Allah (may Allah's peace and blessings be upon him) wiping over the top of his leather socks

عن عبد خير، عن علي رضي الله عنه ، قال: لو كان الدين بالرأي لكان أسفل الخُفِّ أولى بالمسح من أعلاه، وقد «رأيت رسول الله صلى الله عليه وسلم يمسح على ظَاهر خُفَيْهِ».
[صحيح] - [رواه أبو داود]

‘Abd Khayr (may Allah be pleased with him) reported that ‘Ali (may Allah be pleased with him) said: "If the religion was based on reason, the wiping over the sock would be done underneath rather than the on the top. However, I saw the Messenger of Allah (may Allah's peace and blessings be upon him) wiping over the top of his leather socks."
Sahih/Authentic. - [Abu Dawood]

Explanation

‘Ali (may Allah be pleased with him) said that if the religion were to be based on reason instead of revelation, then wiping the bottom of the socks would be more appropriate than wiping over the top, as the bottom part is what touches the ground and dirt and therefore would make more sense to wipe the bottom. However, Islamic law says the otherwise, and adherence to it is obligatory and anything suggesting otherwise should be disregarded. ‘Ali saw the Prophet (may Allah's peace and blessings be upon him) wiping over the top of his sock. What the Prophet (may Allah's peace and blessings be upon him) did, conforms with common sense from another aspect. That is because, if he wiped the bottom of his sock with water, it would result in it picking up impurities, so instead, he wiped over the top to remove any dust that was stuck there, as the top of the sock is what is seen and thus wiping it makes more sense. Significantly, none of the rulings of Islamic law contradicts sound intellect; however, this is sometimes hidden from people of intellect (humans).