Is fasting required every time one lies after having sworn not to lie? Is joking considered a lie that requires expiation? And does the expiation end once it has been performed by fasting?

An oath is broken by the occurrence of a lie, and expiation becomes obligatory by feeding ten poor people, or clothing them, or freeing a slave, or fasting for three days if unable to perform the previous options. This expiation atones for the oath once, unless another oath is sworn, or the wording of the oath implies repetition, or that was intended.

Lying is informing about something contrary to its reality, and it includes jesting; because the Prophet, peace and blessings be upon him, said: "I guarantee a house in the middle of Paradise for one who abandons lying, even if it is in jest." He also threatened with woe the liar who makes people laugh, and warned against lying, whether serious or in jest.