Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "A person should not sit between a man and his son in a gathering."
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator whom I do not know.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 12932