Musnad Ahmad 27:426

Yazid narrated to us, Muhammad ibn Ishaq informed us, from Nafi’, from Ibn Umar, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade that two people whisper to each other excluding a third, if there is no one else with them." He said: And the Prophet (peace and blessings of Allah be upon him) forbade that a man displace another man from his seat, and he said: "If he returns, he is more entitled to it."