Sayyiduna Uqbah bin Amr (Abu Mas'ud) (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) used to wipe our shoulders in the prayer and say: "Keep your shoulders level, straighten the rows, and do not differ, lest your hearts differ."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14670