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

There is meat that was slaughtered for a Buddhist person who bought it
(the animal) inorder 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 whoslaughtered it was a Muslim
and he slaughtered it in the Islamic way. Is it permissible to eat
it?.
Praise be to Allaah.
If it was slaughtered purely for the meat, as isthe 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 mentionedover it, it is not permissible to
eat it. Allah says (interpretationof the meaning):
"So eat of that (meat) onwhich Allaah's Name has been pronounced
(whileslaughtering the animal), if you are believers in His Ayaat
(proofs, evidences, verses, lessons, signs, revelations, etc.).
119. And why should younot eat of that (meat) onwhich Allaah's Name
has been pronounced (at thetime 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 thetime of the slaughtering of the animal), for
sure itis 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 youworshipped
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
(interpretationof 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
thanAllah 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 orassociate. 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 tobe different from them and turn away from their
path, and turn witha 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 (blessingsand 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 isnot 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,
andthe 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 toAllah 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 helpby
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 toanyone 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 Christor 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 tohim, it
is haraam, even ifthe 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 isestablished 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
majorshirk, because sacrifice isan act of worship, so theone 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 Angelsor one of the Messengersor 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 thepale of Islam.
With regard to eating the meat of these sacrifices, it is haraam,
because it was sacrificedto 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 thatthis 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.