There is a restaurant called McDonald’s, which cook food in the oil used for pork. Is it allowed to eat the chicken or beef which they sell, knowing that they are called Ahlul-Kitab?
In the name of Allah, the Most Beneficent, the Most Merciful. May Peace and Blessings be upon the Messenger of Allah and his Companions and all those who follow his guidance. This is not permissible because Allah prohibited pork. Even though what is mentioned in the verse is:
حُرِّمَتْ عَلَيْكُمُ الْمَيْتَةُ وَالْدَّمُ وَلَحْمُ الْخِنْزِيرِ وَمَآ أُهِلَّ لِغَيْرِ اللَّهِ بِهِ
He has forbidden you only the Maytatah (dead animals), and blood, and the flesh of swine, and that which is slaughtered as a scrifice for others than Allah (or has been slaughtered for idols, etc., on which Allah’s Name has not been mentioned while slaughtering)
The flesh of swine includes all the pig, from the flesh or oil and like that. This what the evidences indicate and the understanding of the Salaf, may Allah be pleased with them. The meaning is that they disintegrate the fat or some of it while cooking, but a small amount is prohibited. It is not allowed, whether it is from a person from the people of the Book or from a person who is not from the people of the Book. This food is not allowed if it is cooked in what is remaining from the oil of pork.
Faisal Ibn Abdul Qaadir Ibn Hassan