Musnad Abu Ya'la al-Mawsili 155:51

Ya'qub ibn Ibrahim narrated to us, Muhammad ibn 'Abd al-Rahman al-Tafawi narrated to us, Ayyub narrated to us, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurayrah, who said: "The worst of food is the food of the wedding feast (walimah) to which the rich are invited and the poor are left out. Whoever does not answer the invitation has disobeyed Abu al-Qasim, may Allah bless him and grant him peace."