Riyad as-Saliheen 1599
Ibn Mas'ud (May Allah be pleased with him) said:
The Messenger of Allah ﷺ said, "When three of you are together, two of you must not converse privately ignoring the third till the number increases, lest the third should be grieved."
[Al-Bukhari and Muslim].
وعن ابن مسعود رضي الله عنه أن رسول الله ﷺ قال:
"إذا كنتم ثلاثة، فلا يتناجى اثنان دون الآخر حتى تختلطوا بالناس، من أجل أن ذلك يحزنه" ((متفق عليه)).
Classification
Sahih (Authentic)
References
Riyad as-Saliheen 1599
Riyad as-Saliheen Book of Prohibited actions, Hadith 89