What is the ruling on delaying the fasting of a vow, and is the one who does so rewarded despite the obligation to make it up?

Fulfilling a vow (nadhr (definition)) is obligatory, based on Allah's saying: ﴿And let them fulfill their vows﴾ (Quran 22:29), and the Prophet's (PBUH) saying: "Whoever vows to obey Allah, let him obey Him." A vow contingent upon a condition is prohibited and disliked, because it is not made purely to draw closer to Allah, but rather conditional upon the vow-maker gaining a benefit. Nevertheless, fulfilling it remains obligatory, and the one who fulfills it will be rewarded. Delaying the fulfillment of a vow does not negate its obligation; rather, it remains a liability. Hastening to fulfill a vow is recommended, and delaying it goes against what is better, based on Allah's saying: ﴿So strive in all good deeds.﴾ (Quran 2:148).