Jami` at-Tirmidhi 512
جامع الترمذي#512SahihAbu Hurairah narrated that :Allah's Messenger said: "Whoever said: 'Be quiet' while the Imam is giving the Khutbah then he has committed Laghw (useless activity)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 4:25