A vow to pray two rak'ahs after every obligatory prayer, then abandoning it

Question:
Honorable Shaykh. If a person vows to pray two rak'ahs for Allah after every obligatory prayer, after the one that has just passed, and then he abandons it on some days due to an excuse such as illness or something else, does he owe an expiation for an oath? Does he have to make it up every time he leaves it off, or is making it up once sufficient? And if he abandons it because of the hardship involved, does he owe an expiation for the day he concealed his repentance?

Answer:
This has passed through your studies in the chapter on vows: if a person vows to perform an act of obedience and does not do it, he is required to make it up, and he owes an expiation for an oath for the delay if he specified a time for it. He specified a time here when he said, “I will pray two rak'ahs with every obligatory prayer,” linking it to the prayer. So if he delays it, he is required to make it up because it is obligatory, and his obligation is not discharged except by making up what is obligatory. He is also required to pay an expiation for an oath for the delay.