"When you are three, two should not converse (privately) to the exclusion of their companion, because that makes him sad." (Using translation from Ibn Mājah 3775)
قَالَ رَسُولُ اللهِ ﷺ إِذَا كُنْتُمْ ثَلَاثَةًفَلَا يَتَنَاجَى اثْنَانِ دُونَ الثَّالِثِ إِلَّا بِإِذْنِهِ فَإِنَّ ذَلِكَ يُحْزِنُهُ