Sunan Abi Dawud, Hadith 1112 ⓘ
Abu Hurairah reported the Messenger of Allah as saying: When you tell (your brother on Friday) to be silent while the imam is giving the sermon you are guilty of idle talk.
حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدٍ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا قُلْتَ أَنْصِتْ وَالإِمَامُ يَخْطُبُ فَقَدْ لَغَوْتَ " .
also referenced under: Hadith 1107 (Hasan) & Book 3, Hadith 1107 (USC-MSA)