Musnad Ahmad 1153:1330

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Qatadah, from Mu'adhah al-'Adawiyyah, from 'Aishah, who said: "The Prophet, peace and blessings of Allah be upon him, used to pray the Duha prayer four rak'ahs, and he would increase whatever Allah willed."