As was mentioned in the section about the categories of the Sunnah, working with (and acting upon) the Sunnah is Waajib. The following is a summary of what preceded in respect to the Hukm (ruling) of working with each Sunnah:

1 – Al-Mutawaatir: It is obligatory to take the Sunnah Al Mutawaatirah in respect to the Aqaa’id and the Ahkaam.

2 – Al-Mash’hoor: It is obligatory to take the Mash’hoor in respect to the Ahkaam.

3 – Khabar Al-Aahaad: If it is Saheeh or Hasan, then it is obligatory to be taken to be worked with in respect to the Ahkaam.

4 – As-Sunnah Ad-Da’eefah: It is not used as evidence at all due to its transmission not being verified in respect to it being from the Messenger (saw).

5 – Al-Mursal: The Mursal At-Taabi’iy is used as evidence and acted upon or worked with as long as there is nothing stronger opposing it from like the Mash’hoor and Saheeh amongst others... And this also relates to the Ahkaam (and not the Aqeedah).