Ibn 'Umar (May Allah be pleased with them) said:
the Messenger of Allah ﷺ said, "In the presence of three people, two should not hold secret counsel, to the exclusion of the third."

[Al- Bukhari and Muslim].

In Abu Dawud, Abu Salih related: I asked Ibn 'Umar: "What if there are four people." He said, "There is no harm in that."

Malik reported in Al-Muwatta that 'Abdullah bin Dinar related: Ibn 'Umar and I were together in Khalid bin 'Uqbah's house which was situated in the market place. A man came to consult Ibn 'Umar. None besides me was present. Ibn 'Umar called another man in and we became four and said to me and the man he had called: Move away a bit because I have heard the Messenger of Allah ﷺ saying, "The two people should not hold secret counsel together excluding the third."

وعن ابن عمر رضي الله عنهما أن رسول الله ﷺ قال: "إذا كانوا ثلاثة فلا يتناجى اثنان دون الثالث" ((متفق عليه)).
((ورواه أبو دواد وزاد: قال أبو صالح: قلت لابن عمر: فأربعة؟ قال: لا يضرك. ورواه مالك في الموطأ: عن عبد الله بن دينار قال: كنت أنا وابن عمر عند دار خالد بن عقبة التي في السوق، فجاء رجل يريد أن يناجيه، وليس مع ابن عمر أحد غيري، فدعا ابن عمر رجلا آخر حتى كنا أربعة فقال لي وللرجل الثالث الذي دعا: استأخرا شيئًا، فإني سمعت رسول الله ﷺ يقول: "لا يتناجى اثنان دون واحد".