Hadith 2183

Ibn Umar reported Allah's Messenger (may peace be upon him) as saying: When there are three (persons), two should not converse secretly between themselves to the exclusion of the (third) one.

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ إِذَا كَانَ ثَلاَثَةٌ فَلاَ يَتَنَاجَى اثْنَانِ دُونَ وَاحِدٍ ‏"‏ ‏.‏

Reference: 358600
In-book reference: Book 39, Hadith 2183 a
Hadith 2183 - The Book of Manners and Etiquette - Sahih Muslim - Sunnah.com