Malik bin Abi Amir narrates from Uthman bin Affan (may Allah be pleased with him) that he used to say in his sermon, and he seldom left it out whenever he delivered a sermon: When the imam stands to deliver the sermon on Friday, listen attentively and remain silent, for the one who remains silent but cannot hear (the sermon) has a share (of reward) like that of the one who listens and remains silent. When the iqamah is called, straighten the rows and align your shoulders, for "straightening the rows is part of the completion of the prayer." Then he would not say the takbir until those who had been appointed to straighten the rows informed him that the rows had been straightened; when they informed him that the rows were straight, then he would begin the prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5835