Musannaf Ibn Abi Shayba 35:45

Abu al-Ahwas narrated to us, from Simak, from Ikrimah, from Ibn Abbas, who said: One of the wives of the Prophet, may Allah bless him and grant him peace, performed ghusl (ritual bath) in a large basin. The Prophet, may Allah bless him and grant him peace, came to perform ghusl in it or to perform wudu (ablution) from it. She said: "O Messenger of Allah, may Allah bless him and grant him peace, I was in a state of janabah (major ritual impurity)." He said: "Indeed, water does not become ritually impure."