What is the ruling on someone who vows to memorize the entire Qur’an or not to abandon it, then doubts his vow, and what is the expiation for a vow when it is impossible to fulfill it?

If you are unsure between two vows, investigate which one you made and adhere to it. If nothing becomes clear to you, then the more cautious approach is to fulfill the more comprehensive vow, which is memorizing the entire Qur’an. If you are unable to fulfill it, then its expiation is the expiation for an oath: feeding ten poor people, or clothing them, or freeing a slave; and if you cannot find that, then fasting for three days.