An oath sworn deliberately by Allah is binding, and if you break it the expiation fixed by Allah is: feeding ten poor people from the average of what you feed your family, or clothing them, or freeing a slave; whoever is unable to do any of these fasts three days (Qur'an 5:89). Allah also says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame for what your hearts have earned" (Qur'an 2:225), so casual expressions like "wallāhi" said without intent carry no expiation. If you swore to do something and then realise a better course, the Sunnah is to do what is better and expiate for the oath — the Prophet ﷺ said, "Whoever takes an oath and then sees something better than it, let him do that which is better and expiate for his oath." Note also that swearing by anything other than Allah — the Prophet, one's life, one's mother — is prohibited; the Prophet ﷺ said, "Whoever swears by other than Allah has committed disbelief or shirk," which the scholars explain here as minor shirk. Breaking such a statement carries no kaffārah; one repents instead.
Q&A · Rulings
What is the expiation (kaffārah) for breaking an oath?
Evidence — the daleel
Quran 5:89Quran 2:225Sahih Muslim 1650 (Kitab al-Ayman) — "He who takes an oath and then finds something better than it, let him do that which is better and expiate for his oath" ṢaḥīḥJami' at-Tirmidhi 1535 (sahih) — Ibn Umar: "Whoever swears by other than Allah has committed disbelief or shirk"
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.