It is narrated from Sayyiduna Bara bin Azib (may Allah be pleased with him). He says that the Messenger of Allah (peace and blessings of Allah be upon him) would come to one side of the row and straighten the chests and shoulders of the worshippers and would say: "Do not differ among yourselves, lest your hearts also differ. Surely, Allah Almighty and His angels send blessings upon the first rows."