Tamim bin Tarafah narrates that Sayyiduna Jabir bin Samurah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "Will you not form rows the way the angels who are with their Lord form rows?" The people said: How do the angels who are with their Lord form rows? He said: "They keep the front rows straight and stand close together in the row."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1800