Musannaf Ibn Abi Shayba 1:353

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