Maliks Muwatta Book 28, Hadith Number 50.
Section : The Wedding Feast.
Yahya related to me from Malik from Ibr. Shihab from al-Araj that Abu Hurayra said, “The worst food is the food of a wedding feast to which the rich are invited and the poor are left out. If anyone rejects an invitation, he has rebelled against Allah and His Messenger.”