Sahih Muslim
Sahih Muslim 2183 a
The Prohibition Of Two People Conversing Privately To The Exclusion Of A Third Without His Consent
Arabic hadith text
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 " .
Translation
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.