What is the expiation for one who swore an oath upon the Qur’an not to return to a sin, then returned to it, while not remembering whether he said "in sha’ Allah" (if God wills) or not, and should he fast or feed the poor from the money he has available, and is it permissible to feed them in installments?

The cure for sin lies in repentance, remorse, abandoning the sin, and resolving never to return to it. Doubt about the existence of an exception does not remove the ruling of expiation unless that exception is customary for the person, in which case no expiation is due from him. If expiation becomes obligatory and there is no exception, then it must be paid from what the person owns. Fasting is not permissible if feeding or clothing ten needy persons is available, and they can be fed in installments.