Is it permissible to wipe over socks?

Wiping over socks is a Sunnah if they are strong and thick. The obligatory part for wiping is their top, due to the Hadith of Ali, may Allah be pleased with him: "Had the religion been based on opinion, the sole of the leather sock would have been more worthy of being wiped than its top. But I saw the Messenger of Allah, peace and blessings be upon him, wipe over the top of his leather socks."