Dear Hadi,
Dear Reader,
We will offer a detailed answer, perhaps more than you asked for, since we are sure that the issue you raise is faced by many. This is our opinion, not a fatwa, and Allah SWT knows best.
While the goal of the oath you took is of course commendable, it seems you took an oath that has proven too difficult to fulfill. And your parents perhaps see this and that is why they are not allowing you to fast that many days.
There is a hadith from the Prophet (pbuh) that says, “If you take an oath to do something and then find a better alternative, you should adopt the latter and expiate for your oath” (Al-Bukhari and Muslim).
We recently answered a similar question from someone who asked about the expiation for an oath that was broken. We have pasted the answer we gave to that question below:
Allah SWT knows that although we may have the best of intentions, we sometimes fall short, even when we make promises to Him. Out of His mercy, He has explicitly provided a way for us to atone for such broken promises.
In Islam, the atonement for breaking an oath is called kaffarat al-yamin (“expiation for an oath”). The specifications for how to fulfill this expiation are mentioned in the Quran in Sura Al-Ma’ida (5:89):
God will not take you to task for oaths which you may have uttered without thought, but He will take you to task for oaths which you have sworn in earnest. Thus, the breaking of an oath must be atoned for by feeding ten needy persons with more or less the same food as you are wont to give to your own families, or by clothing them, or by freeing a human being from bondage; and he who has not the wherewithal shall fast for three days [instead]. This shall be the atonement for your oaths whenever you have sworn [and broken them]. But be mindful of your oaths! Thus, God makes clear unto you His messages, so that you might have cause to be grateful. (Muhammad Asad translation)
Please note that the allowance to fast for three days is only in the event that the individual is unable to fulfill one of the previously mentioned options (feeding ten needly people, clothing ten needy people, or freeing someone who is enslaved).
We encourage you to expiate your oath following the above verse, and then consider yourself done with it, rather than continuing to tally more and more fasting days. Ask Allah SWT for forgiveness, in that your intentions were good, but that you took on more than you could handle, and rely on His mercy. In gratitude for, and trust in, that mercy, continue making your best efforts to maintain your prayers.
There are two other issues to bring up:
The first is that you should honestly explore with yourself why you would (to use your words) intentionally miss a fard salat. Do you really mean intentionally without excuse, or are you being too hard on yourself? For example, there was no easy opportunity to offer the prayer, or that you were just pre-occupied, etc. If you have an excuse, trust in God’s mercy. If indeed you have no excuse at all, and simply decided not to pray, gently but firmly remind yourself of the teachings of the Quran and the Hadith:
“Then there came after them successors who neglected prayer and followed desires, so they will face destruction.” (Qur’an 19:59)
“So woe to those who pray—those who are heedless of their prayer.” (Qur’an 107:4–5)
“Indeed, prayer has been decreed upon the believers at fixed times.” (Qur’an 4:103)
“Between a man and disbelief (kufr) and polytheism is abandoning the prayer.” Hadith of the Prophet (pbuh) in Ṣaḥiḥ Muslim.
The second issue is what to do with the prayer that you missed. The majority view of the scholars is that you should make it up as soon as you can, so that your prayer record is complete, relying on the hadith of the Prophet (pbuh), reported in Sahih al-Bukhari:
"If anyone forgets a prayer, he should pray that prayer when he remembers it. There is no expiation except to pray the same." Then he recited: "Establish prayer for My (i.e. Allah's) remembrance." (part of the Quranic verse 20:14).
This is for unintentional forgetting of the prayer, and scholars say that by analogy, intentional omission is more deserving of repayment than unintentional omission.
For completeness, a minority view is that since the omission was intentional, it is not covered by this hadith, and the only expiation is sincere repentance. However, we find this view too restrictive, and God knows best.
So, in summary, our view is:
1. Expiate your oath according to the verse from Sura Al-Ma’ida quoted above.
2. Examine with yourself why you would intentionally miss a prayer, and try to get yourself to a position where you will not do that (to the best of your ability).
3. If you miss a prayer, make it up and ask Allah SWT for acceptance.
In peace.