al-Ma'rur bin Suwayd al-Asadi المعرور بن سويد الأسدي أبو أمية الكوفي · The Chapters on Expiation

"Vows do not bring the son of Adam anything unless it has been decreed for him. But he is dominated by Divine preordainment, and will get what is decreed for him. And (vows) are a means of making the miser give something, so what he desires becomes obtainable for him, which was not obtainable before his vow. And Allah says: 'Spend, I will spend on you.'