Musnad Ahmad 25:946

Abdullah ibn al-Walid narrated to us, he said: Sufyan narrated to us, from Simak, from Ikrimah, from Ibn Abbas: That a woman from the wives of the Prophet, may God bless him and grant him peace, bathed from janabah (major ritual impurity). The Prophet, may God bless him and grant him peace, came to bathe from what remained of her water. She said: "I have bathed from it." The Messenger of God, may God bless him and grant him peace, said: "Indeed, nothing makes water impure."