It was narrated from Khuzaimah bin Thabit that:
The Prophet said: "Three days." I think he said, "And three nights during which the traveler may wipe over his leather socks." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 554 (RU)
Arabic reference (RU): Book 1, Hadith 597 (RU)