Muwatta Malik, Book 28, Hadith 1145 (In-Book)

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."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّهُ كَانَ يَقُولُ شَرُّ الطَّعَامِ طَعَامُ الْوَلِيمَةِ يُدْعَى لَهَا الأَغْنِيَاءُ وَيُتْرَكُ الْمَسَاكِينُ وَمَنْ لَمْ يَأْتِ الدَّعْوَةَ فَقَدْ عَصَى اللَّهَ وَرَسُولَهُ ‏.‏

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also referenced under: Book 28, Hadith 50 (USC-MSA)