Am I obligated to offer expiation (kaffarah) for an oath after swearing by Allah three times to buy a car within days, and I did not fulfill that, and what is the expiation and how is it performed, and am I obligated to fulfill the oath and buy the car?

If a person swears to buy a car within a certain period, and that period passes without him buying it, he is considered a perjurer and is obligated to offer one expiation for a broken oath, due to the repetition of the oath concerning a single matter. It is advised to be diligent in honoring one's parents and to avoid harming them.