Musnad Ahmad 5:555

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from al-Hakam, who said: I heard al-Qasim ibn Mukhaymirah narrating from Shurayh ibn Hani', that he asked 'Aishah about wiping over the leather socks (khuffayn). She said: "Ask 'Ali about that, for he used to go on military expeditions with the Messenger of Allah, may Allah bless him and grant him peace." So he asked him, and he said: "For the traveler, three days and their nights, and for the resident, a day and a night." It was said to Muhammad: "Did he attribute it to the Prophet (marfu')?" He said: "He used to consider it to be attributed (marfu'), but he was hesitant about it."