Musnad Abu Ya'la al-Mawsili 110:275

Zuhayr narrated to us, Abu Mu'awiyah narrated to us, from al-Hajjaj, from al-Hakam, from Yahya ibn al-Jazzar, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) prayed in an open space, with nothing in front of him.