Musnad Ahmad 1153:1956

'Abd al-A'la narrated to us, Sa'id and Yazid narrated to us - he said: Sa'id informed us - from Qatadah, from Safiyyah bint Shaybah, from 'Aishah, that the Prophet, peace and blessings of Allah be upon him, used to perform ghusl with a sa' and perform wudu' with about a mudd. Yazid said, from Safiyyah bint Shaybah, or Mu'adhah.