What should I do, as I have vowed to complete the entire Qur'an in one night (Qiyam al-Layl), but was unable to do so?

This vow, which is contingent upon a condition, must be fulfilled once its condition is met. If you are unable to fulfill it due to an excusable reason that is likely to be removed, then wait for its removal and thereafter fulfill your vow. However, if the inability is not likely to be removed, then the expiation for the vow is the expiation for an oath, which is feeding ten poor people, or clothing them, or freeing a slave. If you cannot find any of these, then it is fasting for three days.