Zirr bin Hubaysh (may Allah have mercy on him) says: I came to Safwan bin Assal al-Muradi (may Allah be pleased with him) and said: Something troubles my heart about wiping over the leather socks after relieving oneself and urinating, and you are a Companion; I have come to you to ask whether you heard anything about this from the Messenger of Allah (peace and blessings be upon him). He said: Yes, he (peace and blessings be upon him) used to command us: "When we are travellers, we should not take off our leather socks for three days and three nights except for major ritual impurity (janabah); and we should not take them off for relieving oneself, urine or sleep."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 577