Musnad Ahmad 27:1356

'Affan narrated to us, Wuhayb narrated to us, Ayyub narrated to us, from Nafi', from Ibn 'Umar, from the Prophet (peace and blessings of Allah be upon him), who said: "When the dinner is served and the prayer is established, then begin with the dinner." He said: And Ibn 'Umar once ate dinner while he was hearing the recitation of the Imam.