Musnad Ahmad 1153:1818

Bahz narrated to us, he said: Hammad ibn Salamah narrated to us, he said: Qatadah informed us, from Mu'adhah, or Safiyyah, from Aisha, that the Messenger of Allah (peace and blessings of Allah be upon him) used to perform ghusl with a sa' and perform wudu with a mudd.