System of Islam by Taqiuddin an-Nabhani

The AHkam shar’aiah are divided into: the fard (compulsory), the haram (prohibited), the mandoob (recommended), the makruh (undesirable) and the Mubah (permissible). The Hukm shar’ai is either an order to perform an action or to abstain from performing an action. If the order (amr) to perform the action is decisive (jazim), then it is classified as fard or wajib. Both these terms are synonymous. If the amr to do an action is indecisive, it is classified as mandoob. If the order to abstain is decisive, it is classified as haram or maHzur which are synonymous, whereas if the order to abstain is indecisive (ghair jazim), it is classified as Makruh. Thus, with the fard/wajib, the performer is praised and the one who abstains from it is condemned. The person who neglects to perform the fard deserves to be punished. The person who performs the haram is condemned and the one who abstains from it is praised. The person who performs the haram deserves to be punished. The person who performs the mandoob is praised and rewarded and the one who abstains is not condemned i.e. he is rewarded for performing the action and not punished for abstaining from it. The person who does not perform the makruh action is praised and rewarded i.e. abstaining from the makruh is preferable. The mubah is which the daleel as-Sam'ai (textual evidence) shows that the speech of the Legislator implies the choice between performing an action or abstaining from it.