Musannaf Ibn Abi Shayba 3:3634

Abu Bakr narrated to us, he said: Isma'il bin Ibrahim narrated to us, from Layth, from al-Hajjaj bin 'Ubayd, from Ibrahim bin Isma'il, from Abu Hurayrah, from the Prophet (peace be upon him), who said: "Is one of you unable, when he has prayed, to move forward, or move backward, or to his right, or to his left?" meaning the voluntary prayer (al-subhah).