Is expiation and repentance both obligatory for someone who swore a false oath (yamin ghamus) in order to achieve a surprise for his mother, and is such an oath forgivable?

The "yamin (definition) ghamus" (a false oath sworn deliberately to seize another's right) is one of the major sins. It necessitates sincere repentance, characterized by remorse, cessation of the sin, and a firm resolve not to return to it. The majority of scholars hold that expiation (kaffarah (definition)) is not obligatory for the yamin ghamus, while Imam Shafi'i deemed it obligatory, and it is also one narration from Imam Ahmad. If one repents sincerely, Allah accepts repentance and forgives sins. However, if one wishes to be cautious by offering an oath expiation, that is commendable.