Hadith 4965
وَعَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا كُنْتُمْ ثَلَاثَةً فَلَا يَتَنَاجَى اثْنَانِ دُونَ الْآخَرِ حَتَّى تَخْتَلِطُوا بِالنَّاسِ مِنْ أَجْلِ أَن يحزنهُ» . مُتَّفق عَلَيْهِ
Abdullah bin Mas'ud (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "When you are three, then two of you should not converse secretly excluding the third until you join other people, for this manner will grieve him (the third person)." Agreed upon.