Musannaf Ibn Abi Shayba 3:2634

Abu Usama narrated to us, from Yahya ibn Maysara, who said: I asked Amr ibn Murrah about the ritual bath (ghusl) on the day of Friday: "Is it a Sunnah?" He replied: "The Muslims used to perform the ritual bath." I repeated the question to him, and he did not add anything more to me than saying: "The Muslims used to perform the ritual bath." So I realized that it was something the Muslims considered recommended, and it was not a Sunnah.