Is it Permissible for One to Eat from what He has Dedicated?

Question :

If a man makes a vow and fulfills it, may he eat from it or not?

Answer:

The basic principle is that the thing which was dedicated in the vow if it was something lawful should be distributed in the area specified by the one who made the vow. If he did not specify any area, then it is a charity which may be disbursed wherever charities are disbursed, such as among the poor and needy. As for eating from it, if the custom in the country of the one who took the vow is that when a person dedicates something he may eat from it himself, then it is permissible for him to eat from it in accordance with tradition and custom in the matter. Likewise, if he made the intention to eat from it and the custom is particular to the part from which he eats, then it is not included in the thing which was dedicated. The Committee has issued a legal verdict on this, the text of which is:

The disbursement of the vow must be in accordance with the intention of the one who made the oath, within the limits of the purified Islamic Law. If he intended that the meat which he dedicated be given to the poor, then it is not permissible for him to eat from it. But if he intended by his vow that his family or his companions of whom he is one eat from it, then it is permissible for him, as one of them, according to the saying of the Prophet ﷺ :
"Deeds are according to intentions and every person shall have what he intended."

Likewise if he made it a condition in his oath or that was the custom in his country.

Source:
Fatawa Islamiyah, Vol. 6 Pages 409-410