Praise be to Allah.
Firstly:
We have stated on several occasions that vows connected to conditions are makrooh, because of the report narrated by al-Bukhaari (6608) and Muslim (1639) from Ibn ‘Umar (may Allah be pleased with him) who said: The Prophet (blessings and peace of Allah be upon him) forbade making vows and said: “They do not avert anything, all they do is get something out of a stingy person.”
If a person wants to obey Allah and draw close to Him, he should obey Him without making vows.
See the answer to question no. 95387
Secondly:
Oaths and vows depend on the intention of the one who makes them.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked about an elderly woman who said that fifty-five years ago she became very sick, then one day she recovered and she said out of joy, I shall offer charity and make a vow, and she said that she would fast for two consecutive months. She says: At that time I did not know what a vow meant and what the consequences would be for me. What should she do about her vow to fast for two consecutive months without knowing what a vow means and what its consequences are?
He replied:
What appears to be to be the case is that this woman does not have to do anything, because so long as she did not know what a vow was, she is not obliged to do something that she did not understand the meaning of. But I think that she must have had something in mind, otherwise her words were just idle talk. So we say that if she had something in mind at that time, then what she had in mind is what she must do, because what counts is the intention. But if she did not have anything in mind and she did not know what it meant at all or what a vow meant, then it seems to me that she does not have to do anything. But if she does fast that will be more on the safe side and more certain that she will be absolved of responsibility. End quote.
Jalasaat Ramadaaniyyah, 21/17
Thirdly:
There should not be any vow to do something that Allah has enjoined upon people. al-Mirdaawi (may Allah have mercy on him) said in al-Insaaf (11/118) (see also Badaa’i‘ as-Sanaa’i‘, 5/90):
“It is not valid with regard to something impossible or something obligatory. If he says, “I promise Allah that I will fast yesterday or that I will fast Ramadan,” it does not count. It is not valid to make a vow concerning something impossible or obligatory, according to the correct opinion. This is the view of our companions. End quote.
Based on the above:
If you did not know that what is meant by the word jamaa‘ah is praying in the mosque with the congregation (jamaa‘ah) of worshippers, and you did not intend that in your vow, then you do not have to do anything.
If your aim was to force yourself to offer one of the prayers on Friday, and you used not to pray at that time, then in fact what you have to do is offer all the five daily prayers on Fridays and on all other days, because Allah has enjoined that upon His slaves, and your vow does not imply anything in addition to that.
You should also strive hard to offer a lot of supererogatory (naafil) and voluntary prayers to make up for the shortfall and your prior negligence towards the obligatory prayers.
And Allah knows best.
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