Musnad Ahmad 1156:277

Ali ibn Ishaq narrated to us, he said: Abdullah—meaning Ibn al-Mubarak—narrated to us, he said: Sa’id ibn Yazid, who is Abu Shuja’, informed us, he said: I heard Abd al-Rahman ibn Hurmuz al-A’raj saying: Na’im, the freed slave of Umm Salamah, narrated to me that Umm Salamah was asked: "Does a woman bathe with a man?" She said: "Yes, if she is clever. I saw myself and the Messenger of Allah, may Allah bless him and grant him peace, bathing from a single basin. We would pour [water] over our hands until we cleansed them, then we would pour the water over ourselves."