Abdullah bin Dinar narrates: I was sitting with Sayyiduna Abdullah bin Umar (may Allah be pleased with them both). Another person was with me. Another man came and started talking with them, so Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said to both of these gentlemen: "You both move aside. The Noble Prophet (peace and blessings be upon him) has said: 'Two people should not converse secretly with each other leaving out the third.'"
Hadith Referenceصحیح ابن حبان / كتاب البر والإحسان / 581
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الصحيحة» -أيضا-.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط البخاري، رجاله ثقات رجال الشيخين غير الحوضي - وهو حفص بن عمر - فمن رجال البخاري.