It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Prophet (peace and blessings of Allah be upon him) said: "It is not lawful for a man to separate two people sitting together by sitting between them, except with their permission."
Hadith Referenceالادب المفرد / كتاب المجالس / 1142
Hadith Gradingالألبانی:حسن
Hadith Takhrij«حسن : أخرجه أبوداؤد ، كتاب الأدب : 4845 و الترمذي : 2752»