Is expiation obligatory upon one who swore an oath with the intention of doing something for a specific period, and that period ended without him doing it?

If a Muslim swears to do something and intends to do it within a specific period, then that period ends and he has not done what he swore to do, he has broken his oath and an expiation for the oath (kaffarat yamin) becomes obligatory upon him. The expiation for an oath is: feeding ten poor persons, or clothing them, or freeing a slave. If he cannot find any of these, then he must fast for three days.