Is it obligatory to obey one's parents if they order their son to shave his beard, justifying it by saying that shaving the beard is disliked in the Shafi'i school of thought, and that letting it grow out is an act of extremism?

The fundamental principle is that parents do not have the right to object to their child's adherence to the Prophetic Sunnahs and manners, because their obedience does not supersede the obedience of Allah and His Messenger, as stated in His Almighty saying: "And why should not some party from every division of them go forth to obtain understanding in religion?" (At-Tawbah (definition): 122). The child should apologize to their parents with kind words and a good approach, while emphasizing the virtue of the Sunnah (definition), and compensating for the lack of obedience with a service or a gift. Letting the beard grow was commanded by the Prophet, peace and blessings be upon him, and parents should not interfere in this, unless letting it grow in a specific country leads to harm and danger; in such a case, it is advised to obey them out of mercy for them.