Musnad Ahmad 27:1689

Yahya ibn Abd al-Malik ibn Abi Ghaniyah narrated to us, my father narrated to us, from Jabalah ibn Suhaym, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you eats with his companion, let him not pair [dates] together until he asks his permission." Meaning: [eating two dates at once].