Musnad Abu Ya'la al-Mawsili 109:169

Abu Bakr ibn Zanjawayh narrated to us, Abd al-Razzaq narrated to us, Ma'mar informed us, from Abdullah ibn Muhammad ibn Aqil, from Jabir, who said: The Prophet (peace and blessings of Allah be upon him) said: "From the perfection of the prayer is the straightening of the row."