It is narrated from Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said regarding wiping over the leather socks (khuffs): "For the traveller it is three days and three nights."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3745