Musnad Ahmad 1153:1603

Yahya narrated to us, Hisham narrated to us, he said: My father informed me, Aisha informed me, she said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "When dinner is served and the prayer is established, then begin with dinner." Waki' said: "When the prayer and dinner are both present." Ibn 'Uyaynah said: "When dinner is served."