Sahih Muslim Book 2, Hadith Number 528.

Chapter : Wiping over the socks.

Mughira b. Shu’ba reported: The Messenger of Allah (may peace be upon him) went out for relieving himself. When he came back I brought for him a jar (of water) and poured water upon his hands and He washed his face. He tried to wash his forearms, but as the (sleeves of the) gown were tight. He, therefore, brought them out from under the gown. He then washed them, wiped his head, and wiped his socks and then prayed.