Slaughtering For Other Than Allah is Shirk

Question :

If a man slaughtered a sheep or some other grazing animal and he said; "O Allah! Place the reward of it in the record of Shaikh So-and-so," is there anything of an innovatory nature in that?

Answer:

If a man slaughters a sheep or some other grazing animal and he gives charity with it on behalf of a deceased person, there is no objection to that. But if he slaughtered it in order to glorify that deceased person and to get nearer to him, then he is a polytheist, guilty of major Shirk. This is because slaughter is an act of worship and a means of seeking closeness and worship and seeking closeness are not for anyone except Allah, as He, Most High says:
"Say (O Muhammad): "Verily, my Salāt (prayer), my sacrifice, my living, and my dying are for Allah, the Lord of the 'Alamin (mankind, jinn and all that exists)." "He has no partner. And of this I have been commanded, and I am the first of the Muslims."

So it is necessary to distinguish between the two intentions: If the slaughterer intended to give charity with its meat in order that this dead person receive the reward of it, then there is no objection to this. Although, it would be better and more fitting if he supplicated for the deceased if he has the right to supplication, i.e., if he was a Muslim. And a person's charity should be for himself, because the Prophet said:
"When a man dies, his deeds are cut off, except three: Continuing charity, or knowledge from which benefit is derived, or a righteous son who supplicates for him."

He did not say to give charity on his behalf, or to fast on his behalf or to pray on his behalf, so this proves that supplication is better and preferred. And you, a living person, are in need of the deed, so make the deed for yourself and make the supplication for your dead brother.

However, if his intention in slaughtering for so-and-so was to draw nearer to him and to glorify him, then it is Shirk, major Shirk, because it is dedicating something of worship to other than Allah, Most High.

Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 6 Pages 258-259-260