Is it permissible to fast in expiation for oaths made before the [current] action, knowing that feeding [the poor] is obligatory and that giving money is not permissible?

You must offer expiation for breaking an oath by feeding ten needy people, or clothing them, or freeing a slave. If you are unable to do so, then fast for three days for each oath. The determining factor for when to perform the expiation is your ability to feed or clothe. It is permissible to delegate someone to perform the expiation on your behalf. It is also permissible to give the monetary value of the expiation according to some scholars, especially if it is more beneficial for the needy.