In a company of three, two should not speak privately leaving out the third in their presence

the Prophet ﷺ said, "When there are three persons, then two of them should not speak privately excluding the third."

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ: «إِذَا كَانُوا ثَلاَثَةٌ فَلاَ يَتَنَاجَى اثْنَانِ دُونَ الثَّالِثِ۔»