Musnad Ahmad 5:186

Yazid narrated to us, from al-Hajjaj, from al-Hakam, from al-Qasim ibn Mukhaymirah, from Shurayh ibn Hani, who said: I asked Aisha about wiping [over the socks/footwear]. She said: "Ask Ali, for he is more knowledgeable about this than I am; he used to travel with the Messenger of Allah, peace and blessings of Allah be upon him." He said: So I asked Ali, and he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "For the traveler, three days and their nights, and for the resident, a day and a night."