Sunan Ibn Majah, Chapter: The Chapters of Purification and its Sunnah

in whose house the Messenger of Allah (saw) performed prayer facing both prayer direction, that he said to the Messenger of Allah (saw): "Can I wipe over my leather socks?' He said: "Yes." He said: "For one day?" He said: "For two days." He said: "For three?" And so on, until the number reached seven. He (the Prophet (saw)) said: "For as long as you see fit." (Daif)