Praise be to Allah.
Sacrifice is an act of worship, and worship can only be done for Allaah alone; the one who does it for anyone other than Allaah is a mushrik (polytheist). Allaah 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’”
“Forbidden to you (for food) are: Al‑Maitah (the dead animals — cattle — beast not slaughtered), blood, the flesh of swine, and that on which Allaah’s Name has not been mentioned while slaughtering (that which has been slaughtered as a sacrifice for others than Allaah, or has been slaughtered for idols) and that which has been killed by strangling, or by a violent blow, or by a headlong fall, or by the goring of horns — and that which has been (partly) eaten by a wild animal — unless you are able to slaughter it (before its death) ‑ and that which is sacrificed (slaughtered) on An‑Nusub (stone‑altars)”
“Verily, We have granted you (O Muhammad صلى الله عليه وسلم) Al‑Kawthar (a river in Paradise).
2. Therefore turn in prayer to your Lord and sacrifice (to Him only)”
Muslim (1978) narrated that ‘Ali ibn Abi Taalib (may Allaah be pleased with him) said: The Messenger of Allaah (blessings and peace of Allaah be upon him) said: “may Allaah curse the one who offers a sacrifice to anything other than Allaah.”
If a person offers a sacrifice to anyone other than Allaah, whether he mentions the name of Allaah over it or not, it is major shirk that puts one beyond the pale of Islam and the meat slaughtered by him is not halaal; rather it is dead meat and it is haraam to eat it.
Al-Nawawi (may Allaah have mercy on him) said:
As for that which is sacrificed to anyone other than Allaah, what this means is that it is slaughtered in a name other than the name of Allaah, such as one who offers a sacrifice to an idol or to the cross, or to Moosa or ‘Eesa (peace be upon them), 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 a Christian or a Jew. This was stated by al-Shaafa’i, and our companions agreed on that. If, in addition to that, he intended to venerate the one for whom he sacrificed it other than Allaah, may He be exalted, and to worship him, this is kufr, and if the one who offered this sacrifice was a Muslim before that, he becomes an apostate by offering this sacrifice. End quote.
The scholars of the Standing Committee for Issuing Fatwas said:
Offering a sacrifice to anyone other than Allaah is shirk, and the ruling on the meat is the same as the ruling on dead meat: it is not permissible to eat it, even if the name of Allaah was mentioned over it, if it is established that it was sacrificed for someone other than Allaah. End quote.
Fataawa al-Lajnah al-Daa’imah, 1/226
They were also asked:
What is the ruling on offering a sacrifice to a dead person who it is claimed was a wali (close friend of Allaah or “saint”) and on whose tomb a structure has been built?
They replied: Offering a sacrifice to the dead person mentioned, who it is claimed is a wali (close friend of Allaah or “saint”) is a kind of shirk (associating others with Allaah), and the one who offers the sacrifice to the wali is an accursed mushrik, and it is dead meat that it is haraam than a Muslim to eat. End quote.
Fataawa al-Lajnah al-Daa’imah, 1/194
Shaykh Saalih al-Fawzaan said:
The words of Allaah “and that on which Allaah’s Name has not been mentioned while slaughtering (that which has been slaughtered as a sacrifice for others than Allaah, or has been slaughtered for idols)” include two things: that which has been offered as a sacrifice to anyone other than Allaah, even if the name of Allaah has been mentioned over it, and it includes that which has not been slaughtered as a sacrifice, rather it has been slaughtered for meat, but a name other than the name of Allaah has been said over it at the time of slaughter. End quote.
Al-Muntaqa min Fataawa al-Fawzaan, 3/49.
Shaykh Ibn ‘Uthaymeen said:
Offering a sacrifice to anyone other than Allaah is major shirk, because offering a sacrifice is an act of worship, so the one who offers a sacrifice to anyone other than Allaah is a mushrik whose shirk has put him beyond the pale of Islam -- Allaah forbid -- whether he offered that sacrifice 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 shirk or associating partners with Allaah -- may He be glorified and exalted -- and puts him beyond the pale of Islam.
With regard to eating meat from these sacrifices, it is haraam, because the name of Allaah was not mentioned over it while slaughtering and it was offered as a sacrifice to someone other than Allaah, and everything that the name of Allaah was not mentioned over it or that was slaughtered on a stone altar is haraam. End quote.
Majmoo’ al-Fataawa, 2/148.
So you have to advise these people and explain to them the error of what they are doing and the seriousness thereof, and tell them that it is something that puts them beyond the pale of Islam. We ask Allaah to guide them to the right path.
And Allaah knows best.