What should I do after having sworn an oath that if I commit a sin again, I would donate the money designated for Hijrah (emigration for the sake of Allah), and I have indeed committed the sin? Must I spend the money, or is it permissible for me to repent and prepare for Hijrah?

Migration to Islamic countries must continue, for the benefit of migration takes precedence over the harm of breaking an oath. Islamic law prioritizes the stronger benefit. If a person takes an oath and then sees something better than it, let him do what is better and expiate his oath. The Prophet, peace and blessings be upon him, said: "By Allah, if Allah wills, I do not swear an oath and then see something better than it, except that I expiate my oath and do what is better." The questioner should hasten to depart for Islamic countries, with sincerity in repentance and frequent seeking of forgiveness. He also owes an expiation for the oath he broke.