Musnad Ahmad 5:402

Yahya ibn Sa'id narrated to us, from Shu'bah, who said: Al-Hakam narrated to me, from Al-Qasim ibn Mukhaymirah, from Shurayh ibn Hani, who said: I asked 'Aishah about wiping over the leather socks (khuffayn). She said: "Ask Ali ibn Abi Talib, for he used to travel with the Messenger of Allah, may Allah bless him and grant him peace." So I asked him, and he said: "For the traveler, three days and their nights, and for the resident, a day and a night." Yahya said: "He (meaning Shu'bah) used to attribute it to the Prophet (marfu'), then he abandoned that."