It was narrated from Abu Hurairah that:
The Messenger of Allah (ﷺ) said: "Whoever says to his companion on Friday, when the imam is delivering the khutbah: 'Listen attentively,' has engaged in idle talk."
App reference: Book 14, Hadith 38
English reference: Vol. 2, Book 14, Hadith 1402
Arabic reference: Book 14, Hadith 1412