What is the difference between the obligatory sunnah and the recommended sunnah?

Question:
In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, Lord of the worlds, and may peace and blessings be upon the noblest of the prophets and messengers, our master and our prophet Muhammad (peace and blessings be upon him), and upon his family and all his companions. May Allah bless you and benefit us with your knowledge, and may Allah reward you with the best reward for us and for the Muslims. He asks: What is the difference between the obligatory sunnah and the recommended sunnah?

Answer:
In the name of Allah, the Most Gracious, the Most Merciful. The default ruling for commands in the Qur'an or in the Sunnah is that they are obligatory. If Allah commands something, or if the Messenger (peace and blessings be upon him) commands something, the default is that it is obligatory. A command is not shifted from being obligatory to being recommended unless there is other evidence from the verses or from the hadiths. A command may be for permissibility, it may be for obligation, it may be for recommendation, or it may be for permissibility. For example, His saying (Glorified and Exalted is He): So when a command comes after a prohibition, it is for permissibility. However, the default is obligation, unless evidence indicates that it is shifted from obligation, whether from the Book or from the Sunnah.