It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that after the Iqamah and before the opening Takbir, the Messenger of Allah (peace and blessings be upon him) turned his face towards the companions and said: "Straighten your rows, and stand close together, for I see you from behind me."
Hadith Referenceالسنن المأثورة / باب ما جاء في صلاة الخوف / 70
Hadith Takhrijصحیح بخاری، الاذان باب اقبال الامام علی الناس عند تسویة الصفوف، رقم: 719۔