Musnad Abu Ya'la al-Mawsili 150:433

Harun ibn Ma'ruf narrated to us, Ishaq al-Azraq narrated to us, Zakariya ibn Abi Za'idah narrated to us, from Khalid ibn Salamah, from al-Bahiy, from 'Urwah, from 'Aishah, that the Prophet (may Allah bless him and grant him peace) used to remember Allah in all of his states.