ENOfficial
He reported God's messenger as saying, "If people sit in an assembly in which they do not remember God or invoke a blessing on their Prophet, vengeance will descend upon them. If God will He will punish them, but if He wills He will forgive them.” Tirmidhi transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَا جَلَسَ قَوْمٌ مَجْلِسًا لَمْ يَذْكُرُوا اللَّهَ فِيهِ وَلَمْ يُصَلُّوا عَلَى نَبِيِّهِمْ إِلَّا كَانَ عَلَيْهِمْ تِرَةً فَإِنْ شَاءَ عَذَّبَهُمْ وَإِنْ شَاءَ غَفَرَ لَهُمْ» . رَوَاهُ التِّرْمِذِيُّ
sunnah.com