Rules of Making Vow for a Mubah Act
Issue No. 2283- One may not vow performing or leaving a mubāḥ act which is religiously neutral in all respects (it is neither desirable nor disliked even in one aspect). However, if it is better to do or leave it in some respect, and a person makes a vow intending that respect, his vow will be valid. For example, if he makes a vow that he will eat a certain food in order to gain energy for worshipping Allah or that he will abandon eating a certain food that causes bodily weakness for worshipping Allah, his vow in either case will be in order.
