Mustahabb actions are those whose ruling (ahkam) in Islamic law falls between mubah (neutral; neither encouraged nor discouraged) and wajib (compulsory).
One definition is "duties recommended, but not essential; fulfilment of which is rewarded, though they may be neglected without punishment".
[1] Synonyms of mustahabb include masnun and mandub.
Parallels have been drawn between the concept of mustahabb in Islamic law and the concept of supererogatory acts in the Western philosophical tradition.
[2] There are possibly thousands of mustahabb acts,[3] including: