He also said—may Allah sanctify his soul:

As for vows, they are of two kinds: those involving obedience and those involving disobedience. Whoever vows to pray, fast, or give charity must fulfil his vow. But if he vows something that is not an act of obedience—such as pledging oil, wax, funds, or anything else to certain graves, shrines, or similar places—this is a vow involving disobedience. In some respects, it resembles making vows to idols such as al-Lāt, al-‘Uzzā, and Manāt, the third and last. By scholarly agreement, such a vow must not be fulfilled. Some scholars, however, require the expiation prescribed for breaking an oath, including Imam Ahmad and others. Others require nothing; this is the view of Abū Hanīfah and al-Shāfi‘ī.

If a person instead devotes what he pledged to a lawful act of devotion—for example, using the oil to light mosques, which are the houses of Allah, and giving the funds to righteous poor people—this is a righteous deed that Allah will accept from him. Nevertheless, making a vow in the first place is disliked, for it is authentically reported that the Prophet, peace and blessings be upon him, “forbade making vows and said, ‘It brings no good; it merely extracts something from the miser.’”

And Allah knows best.