25-What is the Islamic judgment in relation to making a vow (Nadhr)?
It is permissible to make a vow in matters that are acts of obedience to Allah. Moreover, it is obligatory to fulfill the vow. On the other hand, vows in matters that are Islamically prohibited are not permitted and fulfillment of such a vow is not an obligation.
Suratul-Insan, Ayah 7 means, “They honour and fulfill their vows” The Prophet said, “Whoever vows to obey Allah must obey Him, and whoever vows to disobey Allah must not disobey Him.” (Narrated by al-Bukhariy).