Question 270: A person made a vow to slaughter a sheep or a cow for others besides Allah. It is known that such vow is made for Allaah. When this person slaughtered the sheep or cow, he said “In the Name of Allaah”; is it permissible for us to eat from the meat of such an animal or not? After mentioning the Name of Allaah on slaughtering such an animal, does its meat become pure or impure as he intended to offer it as a sacrificial animal to others besides Allaah? Give us the ruling on this question, may Allah increase you in knowledge!
Answer: It is prohibited to make a vow to slaughter a sheep or a cow for others besides Allaah. Also, a Muslim should not fulfill such a vow, as it is an act of disobedience to Allaah. It was authentically reported that the Prophet (peace be upon him) said: Anyone who vows to obey Allaah should obey Him; and anyone who vows to disobey Allaah should not disobey Him. As for the animal offered as a sacrificial animal to others besides Allaah, it is not permissible for a Muslim to eat from its meat even if the Name of Allaah is mentioned on slaughtering it, as it was slaughtered for others besides Allaah... read more here.