Musnad Ahmad 27:597

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, I heard Ayyub ibn Musa narrating from Nafi', from Abdullah ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Two people must not whisper to each other excluding their companion, and a man must not make his brother stand up from his seat and then sit in it."