Musnad Abu Ya'la al-Mawsili 150:287

'Abd al-Jabbar ibn 'Asim narrated to us, he said: Musa ibn A'yan al-Harrani narrated to me, from al-A'mash, from Ibrahim, from al-Aswad, from 'A'ishah: That the Messenger of Allah (may Allah bless him and grant him peace) used to pray nine rak'ahs at night.