Musnad Abu Ya'la al-Mawsili 106:4

'Amr al-Naqid narrated to us, Hafs bin Ghiyath al-Nakha'i narrated to us, al-Hajjaj narrated to us, from Abu Ishaq, from al-Bara' bin 'Azib, who said: It was asked, "Where did the Messenger of Allah, may Allah bless him and grant him peace, prostrate?" He said: "He used to prostrate between his palms."