Question 21: If a father performs the five daily Salaah (Prayers) and maintains the pillars of Islaam but believes that vowing and slaughtering to those buried in the graves and shrines is permissible, can his son use his money to secure his future or inherit him after his death?
Answer: The belief of a Mukallaf (legally competent person) that vowing or slaughtering sacrificial animals to those buried in graves is permissible, is considered Shirk (associating others with Allaah in His Divinity or worship) which takes him out of the fold of Islaam. He should be asked to repent for three days and to be kept under firm control. If he does not repent, he should be killed. With regard to the son’s reception… read more here.