The worst food is the food of a wedding feast to which the rich are invited and the poor are turned away. Whoever refuses the invitation has disobeyed Allah and His Messenger.
حدثنا عفان حدثنا وهيب حدثنا النعمان بن راشد عن الزهري عن سعيد بن المسيب
شر الطعام طعام الوليمة يدعى لها الأغنياء ويدفع عنها الفقراء ومن ترك الدعوة فقد عصى الله ورسوله
Its isnad is sahih. Numan bin Rashid is trustworthy, though he has some lapses, and scholars have relied on his hadith. This hadith is found in Muslim 2/1054 and 1055, in the Book of Marriage, chapter on the command to accept an invitation, and in Abu Dawud 3/341, no. 3742, in the Book of Foods, chapter on accepting invitations.