When does a recommended act become an obligatory one?

The mandub (recommended) is what the Lawgiver commanded in a non-binding manner. Its doer is rewarded, and its ترك is not punished. This applies specifically when considering individual mandub acts for a single person. However, if an act is mandub in part, it becomes wajib (definition) (obligatory) as a whole, such as the adhan (definition) (call to prayer), congregational prayer, and marriage. This is because their complete abandonment would affect the rituals of Islam and the established practices of the religion.