Hadith 2183
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 " .
Ibn Umar reported Allah's Messenger (ﷺ) as saying:
When there are three (persons), two should not converse secretly between themselves to the exclusion of the (third) one.
Reference : Sahih Muslim 2183a
In-book reference : Book 39, Hadith 48
USC-MSA web (English) reference : Book 26, Hadith 5419