Abdullah bin Dinar (may Allah have mercy on him) says that once I and another person were with Sayyiduna Ibn Umar (may Allah be pleased with them), he called the other man and said: "Both of you should be gentle, the Prophet (peace be upon him) forbade that two people whisper to each other leaving out a third person."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5281
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ : 6288 ، م : 2183 .