It is not permissible to eat meat that was slaughtered for anyone or anything other than Allah, even if the one who slaughtered it mentioned the name of Allah over it
Question

                There is meat that was slaughtered for a Buddhist person who bought it (the animal) in order to slaughter it because of a belief that they have which is contrary to our religion (according to their belief, to drive out evil spirits), but the one who slaughtered it was a Muslim and he slaughtered it in the Islamic way. Is it permissible to eat it?.
Praise be to Allah.
      If it was slaughtered purely for the meat, as is the basic 
      reason for which people slaughter animals, then it must be done in the 
      name of Allah. If the name of Allah was mentioned over it, it is 
      permissible to eat it, if it was slaughtered in the well-known shar‘i 
      manner. If the name of Allah was not mentioned over it, it is not 
      permissible to eat it. Allah says (interpretation of the meaning): 

    “So eat of that (meat) on which Allaah’s Name has been 
    pronounced (while slaughtering the animal), if you are believers in His 
    Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.).

    119. And why should you not eat of that (meat) on which 
    Allaah’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? And surely, many do lead (mankind) astray by 
    their own desires through lack of knowledge. Certainly your Lord knows best 
    the transgressors”

     [al-An‘aam 6:118-119] 

    “Eat not (O believers) of that (meat) on which Allaah’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 Allaah). And 
    certainly, the Shayaateen (devils) do inspire their friends (from mankind) 
    to dispute with you, and if you obey them[by making Al‑Maytah (a dead 
    animal) legal by eating it], then you would indeed be Mushrikoon 
    (polytheists); [because they (devils and their friends) made lawful to you 
    to eat that which Allaah 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 Allaah is polytheism]”

    [al-An‘aam 6:121]

    But if what is intended by slaughtering it is an act of 
    worship, then added to the above conditions is that this sacrifice should 
    have been done for Allah, like all other acts of worship. Allah says 
    (interpretation of the meaning):

    “Say (O Muhammad صلى الله 
    عليه وسلم): ‘Verily, my Salaah (prayer), my sacrifice, my living, and 
    my dying are for Allaah, the Lord of the ‘Aalameen (mankind, jinn and all 
    that exists).

    163. He has no partner. And of this I have been commanded, 
    and I am the first of the Muslims’”

    [al-An‘aam 6:162-163]. 

    Ibn Katheer (may Allah have mercy on him) said: 

    Here Allah is commanding him (the Prophet (blessings and 
    peace of Allah be upon him)) to tell the mushrikeen who worship gods other 
    than Allah and offer sacrifices that are not done in His name, that he 
    differs from them in that; his prayer is for Allah, his sacrifice is in His 
    name alone with no partner or associate. This is like the verse in which 
    Allah says (interpretation of the meaning): “Therefore turn in prayer to 
    your Lord and sacrifice (to Him only)” [al-Kawthar 108:2], i.e., make 
    your prayer and sacrifice sincerely for Him alone. The mushrikeen used to 
    worship idols and offer sacrifices to them, so Allah commanded him to be 
    different from them and turn away from their path, and turn with a sincere 
    intention and devotion to Allah alone. End quote. 

    Tafseer Ibn Katheer (3/381-382) 

    Muslim (1978) narrated that ‘Ali ibn Abi Taalib (may Allah be 
    pleased with him) said: The Messenger of Allah (blessings and peace of Allah 
    be upon him) said: “May Allaah curse the one who offers a sacrifice to 
    anything other than Allaah.” 

    Al-Nawawi (may Allah have mercy on him) said: 

    What is meant by offering a sacrifice to anything other than 
    Allah is that which is slaughtered in the name of anything or anyone other 
    than Allah, such as a sacrifice offered to an idol or the cross or Moosa or 
    ‘Eesa (blessings and peace of Allah be upon them both) or to the Ka‘bah and 
    so on. All of that is haraam and this meat is not halaal, whether the one 
    who slaughtered it is a Muslim or Christian or a Jew. That was stated by 
    al-Shaafa‘i and agreed upon by our companions. If he also intended it as an 
    act of veneration or worship of the one other than Allah to whom he 
    slaughtered it, that is kufr. If the one who slaughtered it was a Muslim 
    before that, he becomes an apostate because of this slaughter. End quote. 

    The one who slaughters a sacrifice for anyone or anything 
    other than Allah, such as one who slaughters it for an idol or to ward off 
    evil spirits -- as they claim -- or to draw close to whatever he worships 
    instead of Allah or to a “saint” (wali) and so on is a mushrik who is beyond 
    the pale of Islam and it is not permissible to eat meat slaughtered by him, 
    whether he mentioned the name of Allah over it or not, because he 
    slaughtered it as a sacrifice to someone other than Allah, and Allah says 
    (interpretation of the meaning):

    “He has forbidden you only the Maytah (dead animals), and 
    blood, and the flesh of swine, and that which is slaughtered as a sacrifice 
    for others than Allaah (or has been slaughtered for idols, on which Allaah’s 
    Name has not been mentioned while slaughtering). But if one is forced by 
    necessity without willful disobedience nor transgressing due limits, then 
    there is no sin on him. Truly, Allaah is Oft-Forgiving, Most Merciful”

    [al-Baqarah 2:173]. 

    Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) 
    said: 

    The apparent meaning of the words “and that which is 
    slaughtered as a sacrifice for others than Allaah” is that whatever is 
    slaughtered for anyone or anything other than Allah, such as if it is said, 
    This is a sacrifice to such and such, and this is the intention, whether the 
    person spoke it out loud or not, is haraam, and the prohibition in this case 
    is clearer than the prohibition on that which was slaughtered by a Christian 
    for meat over which he said the name of Christ and so on. That which we 
    slaughter as an act of worship to draw close to Allah is pure and better 
    than that which we slaughter for meat and mention the name of Allah over, 
    because worshipping Allah by praying to Him and sacrificing to Him is better 
    than seeking help by saying His name at the beginning of every action. By 
    the same token, shirk that involves praying to anyone other than Allah and 
    offering sacrifices to anyone other than Him is worse shirk than seeking 
    help in the name of this other “god” at the beginning of every action. If 
    that over which the name of Christ or al-Zahrah is mentioned is haraam, then 
    that which is sacrificed to Christ or al-Zahrah or is intended as such is 
    even more haraam.  Based on that, if something is slaughtered for someone 
    other than Allah as an act of worship to draw close to him, it is haraam, 
    even if the name of Allah is mentioned over it, as some of the hypocrites of 
    this ummah do, who seek to draw close to the “saints” (awliya’) and stars by 
    offering sacrifices, burning incense and so on. If these people are 
    apostates, then meat slaughtered by them is not permissible under any 
    circumstances, because both reasons are combined in this case  

    End quote from Iqtida’ al-Siraat al-Mustaqeem, 260 

    The scholars of the Standing Committee said: 

    Offering a sacrifice to anyone or anything other than Allah 
    is shirk, and the meat comes under the same rulings as maytah (dead meat), 
    and it is not permissible to eat it even if the name of Allah is mentioned 
    over it, if it is established that it was slaughtered for anyone or anything 
    other than Allah. End quote. 

    Fataawa al-Lajnah al-Daa’imah, 
    1/226 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

    Offering a sacrifice to anyone or anything other than Allah 
    is major shirk, because sacrifice is an act of worship, so the one who 
    offers a sacrifice to anyone or anything other than Allah is a mushrik whose 
    shirk puts him beyond the pale of Islam -- whether he sacrifices that to one 
    of the Angels or one of the Messengers or one of the Prophets or one of the 
    caliphs or one of the awliya’ (saints) or one of the scholars. All of that 
    is associating others with Allah, may He be glorified and exalted, and puts 
    one beyond the pale of Islam. 

    With regard to eating the meat of these sacrifices, it is 
    haraam, because it was sacrificed to something or someone other than Allah, 
    and everything that is sacrificed to something or someone other than Allah, 
    or was sacrificed on a stone altar, is haraam. End quote. 

    Majmoo‘ Fataawa Ibn ‘Uthaymeen, 
    2/148 

    If this Muslim slaughterman knew that this animal that he 
    slaughtered was being slaughtered for someone or something other than Allah, 
    even if he mentioned the name of Allah over it, this is major shirk as 
    stated above. If he slaughtered it and did not know that, rather he was 
    asked to slaughter it and he did so, thinking that they were slaughtering it 
    for meat, then there is no blame on him. 

    And Allah knows best. 

    See also the answer to question number
    44730.