Short answer
Swearing by Allah to something you know is false is called al-yamin al-ghamus (the drowning oath). It is a major sin. In the Hanafi school there is no kaffarah for it: the only way out is sincere tawbah, and returning any right you took by it.
Al-yamin al-ghamus, a deliberate false oath about the past or present, is a major sin. It has no kaffarah in the Hanafi school; it requires tawbah (repentance), and if someone's money or right was taken by it, that must be returned.
Other madhhabs
- Shafi'i
- Kaffarah is due for a false oath as well as tawbah, because the verse on oaths is general.
- Maliki
- Agrees with the Hanafi school: no kaffarah, only repentance.
- Hanbali
- The main position agrees that there is no kaffarah, only repentance.
Explanation
When you say 'wallahi' or 'I swear by Allah' you call Allah as your witness. Doing that for a lie you know is a lie is one of the gravest sins of the tongue. The Prophet ﷺ listed it among the major sins together with shirk, disobeying parents and murder. It is called ghamus, 'the one that drowns', because it drowns the person in sin.
It is even worse when the false oath is used to take something. The Prophet ﷺ said that whoever swears a false oath to take a Muslim's property will meet Allah while He is angry with him. The Quran says those who sell their oaths for a small price have no share in the Hereafter.
In the Hanafi school this oath has no kaffarah. Kaffarah is for breaking an oath about the future. A lie about the past is too serious to be wiped out by feeding ten poor people. What it needs is tawbah:
- stop, and feel real regret before Allah;
- resolve never to do it again;
- correct the lie where it caused harm, and return any money or right you gained by it;
- do good deeds, since good deeds wipe out bad ones.
The Shafi'i school also requires kaffarah. If you want to be cautious, paying it does no harm, but it does not replace repentance. An oath you thought was true and later found to be wrong is not ghamus; that is laghw, and Allah does not hold you to it. For oaths about the future, see kaffarah for breaking an oath.
The evidence
Quran, Surah Aal-i-Imraan 3:77
إِنَّ ٱلَّذِينَ يَشْتَرُونَ بِعَهْدِ ٱللَّهِ وَأَيْمَٰنِهِمْ ثَمَنًۭا قَلِيلًا أُو۟لَٰٓئِكَ لَا خَلَٰقَ لَهُمْ فِى ٱلْءَاخِرَةِ وَلَا يُكَلِّمُهُمُ ٱللَّهُ وَلَا يَنظُرُ إِلَيْهِمْ يَوْمَ ٱلْقِيَٰمَةِ وَلَا يُزَكِّيهِمْ وَلَهُمْ عَذَابٌ أَلِيمٌۭ ﴿٧٧﴾
Indeed, those who exchange the covenant of Allah and their [own] oaths for a small price will have no share in the Hereafter, and Allah will not speak to them or look at them on the Day of Resurrection, nor will He purify them; and they will have a painful punishment.
Those who trade oaths for gain are warned of losing their share in the Hereafter.
Quran, Surah Al-Baqara 2:225
لَّا يُؤَاخِذُكُمُ ٱللَّهُ بِٱللَّغْوِ فِىٓ أَيْمَٰنِكُمْ وَلَٰكِن يُؤَاخِذُكُم بِمَا كَسَبَتْ قُلُوبُكُمْ ۗ وَٱللَّهُ غَفُورٌ حَلِيمٌۭ ﴿٢٢٥﴾
Allah does not impose blame upon you for what is unintentional in your oaths, but He imposes blame upon you for what your hearts have earned. And Allah is Forgiving and Forbearing.
Unintended oaths are forgiven, while what the heart intends is held to account.
Sahih al-Bukhari 6675
Sahih... الكبائر الإشراك بالله وعقوق الوالدين وقتل النفس واليمين الغموس ...
"The major sins are shirk, disobeying parents, killing a soul, and the false oath (al-yamin al-ghamus)."
The deliberate false oath is named among the major sins.
Sahih al-Bukhari 6676
Sahih... من حلف على يمين صبر يقتطع بها مال امرئ مسلم لقي الله وهو عليه غضبان ...
"Whoever swears a binding oath to take a Muslim's wealth will meet Allah while He is angry with him."
A false oath used to take a right is especially grave.
Where the ruling is recorded
- al-Hidaya, Kitab al-Ayman. The ghamus oath is a sin with no kaffarah, only repentance.
- al-Majmu' (Nawawi), Kitab al-Ayman. The Shafi'i view that kaffarah is due for it.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.