Kaffarah of breaking Vow and convenant (نذر و عھد)
1: Vow means making it obligatory upon oneself to do some good act, or to refrain from doing an act which it is better not to do, for the sake of, or for the pleasure of Allah.
2: While making a vow, a formula declaration has to be pronounced, though is not necessary that it should be in Arabic. If a person says: "When the patient recovers from his ailment, it will be obligatory upon me to pay $10 to a poor man, for the sake of Allah," his vow will be in order.
3: If a person does not act according to the covenant made by him, he should give a Kaffarah for it, i.e. he should either feed sixty poor persons, or fast consecutively for two months, or set free a slave.
These laws are according to Aayatullah Sistani's Fataawa.