Question: What is the ruling on vowing or slaughtering for the Awliyaa’ (pious people), or making Tawaaf (circumambulation) around their graves? Who are the Awliyaa’ in the sight of Islaam? Besides, is it permissible that someone asks the Awliyaa’, whether they are alive or dead, to make Du`aa’ (supplication) for them?
Answer: Slaughtering or vowing for the sake of dead people is Shirk (associating others with Allaah in His Divinity or worship). A Walee is a person who obeys Allaah by doing what He commands and avoiding what He prohibits even if he is not supported by Karaamaat (extraordinary events performed by a pious person)… read more here.