Messenger of Allah said: "Whoever said: 'Be quiet' while the Imam is giving the Khutbah then he has committed Laghw (useless activity)."  

أَنَّ النَّبِيَّ ﷺ قَالَ مَنْ قَالَ يَوْمَ الْجُمُعَةِ وَالإِمَامُ يَخْطُبُ أَنْصِتْ فَقَدْ لَغَا قَالَ وَفِي الْبَابِ عَنِ ابْنِ أَبِي أَوْفَى وَجَابِرِ بْنِ عَبْدِ اللَّهِ