Which one of the following actions may be regarded as Mubāℎ?
Acquisition of knowledge
smoking
Salāt ash-shaf
Shaking hands while greeting
Correct answer is D
It refers to an action that is not mandatory, recommended, reprehensible or forbidden, and thus involves no judgement from God.
Assigning acts to this legal category reflects a deliberate choice rather than an oversight on the part of jurists