Musnad Abu Ya'la al-Mawsili 86:2

Abu Musa narrated to us, Abu Dawud narrated to us, Abu ‘Amir narrated to us, from al-Hasan, from Sa‘d, who said: Dates were brought before the Messenger of Allah, may Allah bless him and grant him peace, and they began to pair them (eat two at a time). The Messenger of Allah, may Allah bless him and grant him peace, forbade pairing.