Answer: Praise be to Allaah.
The Sunnah is to make the rows straight, and indeed some scholars have said that making the row straight is obligatory, because when the Prophet (sal-Allaahu ‘alayhe wa sallam) saw a man sticking out his chest he said,
“Make your rows straight or Allaah will alter your faces.” [Bukhaaree, al-Adhaan, 717]
This is a threat and there is no threat except in the case of an action that is haraam or a failure to do something that is obligatory. The view that it is obligatory to make the rows straight is a strong opinion and Bukhaaree (رحمه الله) devoted a chapter to this topic entitled: “Chapter on the sin of one who does not complete the row.” [Bukhaaree, al-Adhaan, chapter 75. al-Fath, 2/245]