Zirr bin Hubaysh (may Allah have mercy on him) says: I came to Safwan bin Assal (may Allah be pleased with him) and said to him: You are one of the Companions of the Messenger; something troubles my heart about whether wiping over the leather socks after relieving oneself and urinating is valid or not, so inform me about it, if you have heard anything from the Messenger of Allah (peace and blessings be upon him). He said: He (peace and blessings be upon him) used to command us: "When you are on a journey, do not take off your leather socks for three days and three nights except for major ritual impurity (janabah); but do not take them off for urine, relieving oneself or sleep."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 557