Musnad Ahmad 944:4

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Salamah ibn Kuhayl, he said: I heard Ibrahim al-Taymi narrating from al-Harith ibn Suwayd, from 'Amr ibn Maymun, from Khuzaymah ibn Thabit, from the Prophet, peace and blessings of Allah be upon him, that he said: "Three days," Shu'bah said: I think he said: "and their nights, for the traveler regarding wiping over the leather socks."