Prohibition of speaking during the Friday sermon

عَنْ أَبِي هُرَيْرَةَ، أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ: إِذَا قُلْتَ لِصَاحِبِكَ يَوْمَ الْجُمُعَةِ أَنْصِتْ‏‏ وَالإِمَامُ يَخْطُبُ فَقَدْ لَغَوْتَ‏‏.‏

Hazrat Abu Hurairah^ra narrated that Allah’s Messnger^sa said, “If you say to your companion, on Friday, while the imam is delivering the sermon [khutbah], ‘Keep quiet’, then you too have engaged in idle talk.”

(Sahih al-Bukhari, Kitab al-jumu‘ah, Bab al-insati yawma al-jumu‘ati wa al-imamu yakhtub, Hadith 934)