It is narrated from Simak (may Allah have mercy on him) that he said: I heard Sayyiduna Nu'man bin Bashir (may Allah be pleased with him) saying that when we stood for the prayer, the Messenger of Allah (peace and blessings be upon him) would level our rows, and when we had become straight, then he (peace and blessings be upon him) would say the takbir.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2291