حَدِيثَ أَبِي هُرَيْرَةَ رضى الله عنه فِي «اَلصَّحِيحَيْنِ«مَرْفُوعًا: «إِذَا قُلْتَ لِصَاحِبِكَ: أَنْصِتْ يَوْمَ اَلْجُمُعَةِ وَالْإِمَامِ يَخْطُبُ، فَقَدْ لَغَوْتَ»
On Friday, when the Imam is delivering the Khutbah (religious talk), if you say to your companion to keep quiet, then indeed you have committed a sin (error/something senseless).