According to shari’ah, hibat al-thawab (هبة الثواب) must involve a well defined subject-matter and this is the opinion of jumhur al-fuqaha (al-jumhur). An unknown subject-matter (iwadh) renders hibah voidable (fasid), and it is then subject to the same ruling on voidable sale (al-ba’i al-fasid).

Shari’ah considers hibat al-thawab a commutative contract (aqd al-muawadhah) or more broadly a form of aqd al-tamleek, similar to the contract of sale (aqd al-ba’i/ aqd al-bay’) and subjects it to the same set of rulings, especially in terms of impermissibility of gharar associated with the subject-matter (mahall) and impermissibility of unilateral, deferred delivery (al-nasi’ah). Furthermore, it is impermissible to embed aqd al-hibah (that of hibat al-thawab) with some contingency like a condition (shart). However, if hibah is made contingent on a condition, then the condition shall be viewed and interpreted as wa’ad (promise), rather than shart.