Sunan Ibn Majah 557

It was narrated from Ubayy bin 'Imarah, in whose house the Messenger of Allah performed prayer facing both prayer direction, that :He said to the Messenger of Allah: "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) said: "For as long as you see fit