Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) reports that the Prophet (peace and blessings be upon him) said: "When they are three people, two should not converse privately to the exclusion of the third; and when three people are on a journey, they should make one of themselves the leader." (Allamah al-Haythami says:) I say: From this Companion, this hadith is mentioned in the Sahih: "Two should not converse privately."
Al-Bazzar recorded it, and its narrators are the narrators of the Sahih, except Ubays bin Marhum, who is thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجهاد / 9307