ما حكم الشرع في امتناع شخص عن فعل شيء أقسم عليه آخر؟ وما الإثم المترتب على ذلك؟

Fulfilling the oath of one who has sworn is commendable and encouraged, as long as it does not involve sin or lead to harm. This is based on what is narrated in the Sahihayn from the hadith of Al-Bara' bin 'Azib (may Allah be pleased with them both), who said: "The Messenger of Allah (peace and blessings be upon him) commanded us to do seven things," and among them he mentioned: "and fulfilling the oath." It is not obligatory for you, and there is no sin upon you nor expiation if you do not do what was sworn upon.