Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Nu’man bin Bashir (may Allah be pleased with him), he says that the Messenger of Allah (peace and blessings of Allah be upon him) turned towards the people and said three times: “Straighten your rows. By Allah! You must certainly straighten your rows, or else Allah, the Exalted, will cause discord among your hearts.”