This is what I had posted in a thread a long time ago:
This is the verse which is taken as a proof for permissibility of meat slaughtered by christians/jews:
5:5. Made lawful to you this day are At_Tayyibât [all kinds of Halâl (lawful) foods, which Allâh has made lawful (meat of slaughtered eatable animals, etc., milk products, fats, vegetables and fruits, etc.). The food (slaughtered cattle, eatable animals, etc.) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them.
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And the following are the verses, which prohibit such meat:
***2:173. 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 Allâh (or has been slaughtered for idols, etc., on which Allâh's Name has not been mentioned while slaughtering). But if one is forced by necessity without wilful disobedience nor transgressing due limits, then there is no sin on him. Truly, Allâh is Oft-Forgiving, Most Merciful.
6:118. So eat of that (meat) on which Allâh's Name has been pronounced (while slaughtering the animal), if you are believers in His Ayât (proofs, evidences, verses, lessons, signs, revelations, etc.).
6:119. And why should you not eat of that (meat) on which Allâh's Name has been pronounced (at the time of slaughtering the animal), while He has explained to you in detail what is forbidden to you, except under compulsion of necessity?
6:121. Eat not (O believers) of that (meat) on which Allâh's Name has not been pronounced (at the time of the slaughtering of the animal), for sure it is Fisq (a sin and disobedience of Allâh). And certainly, the Shayâtin (devils) do inspire their friends (from mankind) to dispute with you, and if you obey them] [by making Al_Maytatah (a dead animal) legal by eating it], then you would indeed be Mushrikûn (polytheists) [because they (devils and their friends) made lawful to you to eat that which Allâh has made unlawful to eat and you obeyed them by considering it lawful to eat, and by doing so you worshipped them, and to worship others besides Allâh is polytheism].***
Therefore, make up your own mind, find out which sequence the ayat were revealed, or find out from someone which evidence is stronger. :)