Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.046B.

Section : The description of the wiping.

After the person completes his ablution and puts on his socks or slippers, it is proper for him to wipe over them later on when he wants to perform ablution. He is permitted to do that for one day and night if he is resident, and for three days and nights if he is a traveller. But if he is in post-sex impurity, he must remove his socks, in accordance with the preceding hadith of Safwan.