FOOD of SHIRK in the Quran
حرمت عليكم الميتة والدم ولحم الخنزير ومااهل لغير الله به والمنخنقة والموقوذة والمتردية والنطيحة ومااكل السبع الا ماذكيتم وماذبح على النصب وان تستقسموا بالازلام ذلك فسق اليوم يئس الذين كفروا من دينكم فلا تخشوهم واخشون اليوم اكملت لكم دينكم واتممت عليكم نعمتي ورضيت لكم الاسلام دينا فمن اضطر في مخمصة غير متجانف لاثم فان الله غفور رحيم
“Forbidden to you (for food) are: … meat of that which has been slaughtered as a sacrifice for others than Allâh, or has been slaughtered for idols, etc., or on which Allâh's Name has not been mentioned while slaughtering,…”
— Quran, Surat Al-Ma'idah 5:3
The food of Christians and Jews has been made lawful for Muslims to eat (so long as it doesn't contain a prohibited substance). Conversely, the food of pagans, polytheists, athiests or those who divert is forbidden. This prohibition is not limited to only meat, but to 'food' in the broadest sense (at-T3am).
اليوم احل لكم الطيبات وطعام الذين اوتوا الكتاب حل لكم وطعامكم حل لهم والمحصنات من المؤمنات والمحصنات من الذين اوتوا الكتاب من قبلكم اذا اتيتموهن اجورهن محصنين غير مسافحين ولامتخذي اخدان ومن يكفر بالايمان فقد حبط عمله وهو في الاخرة من الخاسرين
“Today the good things are permitted you, and the food of those who were given the Book is permitted to you, and permitted to them is your food; Likewise believing women in wedlock, and in wedlock women of them who were given the Book before you if you give them their wages, in wedlock and not in licence, or as taking lovers. Whoso disbelieves in the faith, his work has failed, and in the world to come he shall be among the losers."
— Quran. Surat al-Ma'idah 5:5
Hadith referencing FOOD of SHIRK
Though it is impermissible to eat the food of those who are not People of the Book, pagans, athiests, etc., it is incumbant on Muslims to not reject feeding them.
Prophet Ibrahim had the habit of sharing breakfast with another person. So one day, an old man, a traveler appeared before him, ending his wait for a guest to share his meals. The Prophet invited the old man to breakfast with him. While they were introducing each other, he found that his guest was an idol worhipper. Ibrahim was fiercely opposed to idol worship; he had revolted against his own father earlier. Ibrahim told the man to leave. He waited for another person to share his meal with. According to the tradtion, the Archangel Gabriel appeared and asked Ibrahim why he would not share breakfast with the man. Ibrahim replied that it was because he was an idol worshipper. Gabriel then asked Ibrahim to tell him how old the man was. Then Gabriel asked Ibrahim: "If God can tolerate and provide a man who's been an idolator for his whole long life with food and other things for his survival, then why can’t Ibrahim tolerate him for just one meal? Ibrahim went out to call the traveler back to breakfast with him and apologized to the man.