Musnad Ahmad 1153:849

Ali ibn Ishaq narrated to us, he said: Abdullah informed us, he said: Asim informed us, from Mu'adhah, from Aisha, she said: "I used to perform ghusl (ritual bath) with the Messenger of Allah, may Allah bless him and grant him peace, from a single vessel. He would race me and I would race him, and I would say: 'Leave some for me, leave some for me.'"