The Prophet ﷺ said, "Whoever says to his companion on Friday while the imam is delivering the sermon, 'Be quiet,' has spoken idly."
أخبرنا قتيبة قال حدثنا الليث عن عقيل عن الزهري عن سعيد بن المسيب
عن النبي ﷺ قال من قال لصاحبه يوم الجمعة والإمام يخطب أنصت فقد لغا
Reported by Muslim, Friday Prayer, chapter on remaining silent on Friday during the sermon, no. 851, from Qutayba, and Bukhari, Friday Prayer, chapter on remaining silent on Friday while the imam is delivering the sermon, no. 934, through the hadith of Layth bin Saad, with the same chain. It is also found in Al-Kubra, no. 1728.