سُبْحَانَكَ اللَّهُمَّ وَبِحَمْدِكَ أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا أَنْتَ أَسْتَغْفِرُكَ وَأَتُوبُ إِلَيْكَ

“O Allah, You are pure, I praise You and testify that there is none worthy of worship besides You. I seek forgiveness and pardon from You”.

If there was good talk in the gathering, this dua will seal it and if there was futile and vain talk, then this dua will recompense for it. 

(Tirmidhi Targib)