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Surah 6. Al-An'am
Ayah 120 - 121
120وَذَرُوا۟ ظَـٰهِرَ ٱلْإِثْمِ وَبَاطِنَهُۥٓ ۚ إِنَّ ٱلَّذِينَ يَكْسِبُونَ ٱلْإِثْمَ سَيُجْزَوْنَ بِمَا كَانُوا۟ يَقْتَرِفُونَ
121وَلَا تَأْكُلُوا۟ مِمَّا لَمْ يُذْكَرِ ٱسْمُ ٱللَّهِ عَلَيْهِ وَإِنَّهُۥ لَفِسْقٌ ۗ وَإِنَّ ٱلشَّيَـٰطِينَ لَيُوحُونَ إِلَىٰٓ أَوْلِيَآئِهِمْ لِيُجَـٰدِلُوكُمْ ۖ وَإِنْ أَطَعْتُمُوهُمْ إِنَّكُمْ لَمُشْرِكُونَ
[120-121] And refrain from open sins as well as secret sins: surely those who earn sin shall get the recompense of what they have earned. And do not eat the flesh of the animal over which Allah's name has not been mentioned at the time of slaughter; this indeed is sinful. The satans put doubts and objections into the minds of their friends, so that they should dispute with you,86 but if you obey them, you are surely mushrikin.87
86This is with reference to the different kinds of doubts and objections with which the Jewish scholars used to poison the minds of ignorant Arabs against Islam. According to a tradition of Hadrat `Abdullah bin `Abbas, one of the objections taught by the Jews against the Prophet Muhammad (Allah's peace be upon him) was: "How is it that the one killed by Allah (by natural death) should be unlawful, while the other which is killed by us (by mentioning the name of Allah) should be lawful?" This is an instance of the crooked attitude of those so called people of the Book. They would invent and pose questions like this before the common people so as to poison their minds with doubts and to arm them with weapons to fight with the Truth.
87It is also shirk to acknowledge the Godhead of Allah and at the same time follow the decrees and ways of those who have turned away from Allah. The acknowledgment of the Oneness of Allah demands that one should obey Allah in all aspects of one's life. So much so that if a person believes that someone else also should be obeyed along with Allah, he would be guilty of committing shirk in his creed. And if a person obeys such people as arrogate to themselves the authority of making things lawful and unlawful, in utter disregard of the Guidance of Allah, he would be guilty of practical shirk.