Is expiation obligatory for someone who swore not to smoke cigarettes, watch pornographic films, or speak to girls, then listened to music and forgot whether he had sworn against it or not?

The things the young man swore he would not approach are forbidden, and he must abandon them. If he does them, or some of them, he sins and is liable for expiation (kaffarah). Listening to music is forbidden and must be avoided, and one must repent from it. He is not liable for expiation by listening to it, unless he is certain that he swore not to listen to it.