The first thing that you must do is repent to Allah from all that you have done in transgressing the rights of your Lord, the rights of your own self and the rights of your husband and household. You have to strive, as much as you can, to set straight the things that have been spoiled by your bad conduct and failure to understand matters properly.
Secondly:
There is no expiation for this oath according to the correct scholarly view; rather what is required is to repent to Allah, may He be exalted, and seek His forgiveness. You must also beware of taking the matter of oaths lightly if you are telling the truth, so how about if you are lying?
The Standing Committee was asked:
I am a student in a Salafi Institute belonging to the Jamaa’at Ansaar al-Sunnah al-Muhammadiyyah in Kasla [?], and there is an Eritrean Muslim students union. There are major differences between the union and the jamaa’ah, hence doing activities with them is not allowed, but I participated with them. When the director of the institute found out, he asked me: Are you in the union? I said to him, No. He forced me to swear an oath so I did, but I was with them. Is this oath yameen ghamoos (a false oath) or do I have to offer expiation? Please note that if I had not been forced I would not have sworn an oath, but I regarded that as a case of necessity, because if I had told the truth he would have banned me from the Institute, and it is because of my keenness to seek knowledge that I did that.
The Standing Committee replied:
The oath that you mentioned was a yameen ghamoos, which is a major sin which cannot be expiated because of its seriousness. No expiation is prescribed for it according to the more correct of the two scholarly views; rather what is required is repentance and seeking forgiveness, so you have to repent and ask for forgiveness for it. End quote. Fataawa al-Lajnah al-Daa’imah, 23/133.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) was asked:
I have a brother who got a passport and he wants to get another one, and during the application process the official said to him: Do you swear that you do not have a previously issued passport? He did not see any Mushaf in front of the official, then the official took it out. My brother got scared and swore that he had not taken out any other passport. Please advise us on the ruling concerning this matter and whether he has to offer a sacrifice or is some other expiation sufficient?
He (may Allah have mercy on him) replied:
He has to repent to Allah, may He be glorified and exalted, just as any liar has to repent to Allah, and he has to be sincere in that and regret it, and not do it again.
There is no expiation for a false oath according to the correct opinion. The expiation for vows has to do with those which refer to the future, for example if a person says “By Allah I will not do such and such” or “By Allah I will not speak to So and so.” As for the one who tells a lie, all he has to do is repent to Allah, regret what he has done and give up the sin, and he should sincerely resolve not to do that again, out of sincerity towards Allah and the desire for that which is with Him. Thus Allah will pardon him, because by means of sincere repentance Allah erases sin, as He says (interpretation of the meaning): “And all of you beg Allaah to forgive you all, O believers, that you may be successful” [al-Noor 24:31]. End quote.
Majmoo’ Fataawa Ibn Baaz, 23/115
Ref: Islamqa/info..
And Allah knows best.