Musnad Ahmad 5:343

Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from al-Hakam, from al-Qasim ibn Mukhaymirah, from Shurayh ibn Hani, who said: I asked Aisha about wiping [over the socks]. She said: "Go to Ali, for he is more knowledgeable about that than I am." He said: So I went to Ali and asked him about wiping over the two socks. He said: "The Messenger of Allah (peace and blessings of Allah be upon him) used to command us to wipe over the two socks for a day and a night, and for the traveler for three days."