Musnad Ahmad 1153:966

'Affan narrated to us, he said: Hammam narrated to us, he said: Qatadah narrated to us, he said: Mu'adhah al-'Adawiyyah narrated to me, from 'Aishah, she said: "Command your husbands to wash away from themselves the trace of the privy and urine, for I am shy to command them to do that. Indeed, the Messenger of Allah, peace and blessings of Allah be upon him, used to do it."