It is narrated from Hazrat Nu'man (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) used to straighten the rows (in prayer) as if he were straightening arrows among our rows. Once, when the Noble Prophet (peace and blessings be upon him) intended to say the takbeer, he saw that a man's chest was protruding. The Noble Prophet (peace and blessings be upon him) said: "Keep your rows straight (aligned), otherwise Allah will create discord among you."