What is the ruling when a person who has not yet performed the obligatory Hajj (Hajja al-Islam) enters the state of Ihram for a supererogatory Hajj or a vowed Hajj?

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If a person who has not performed the obligatory Hajj enters Ihram for a supererogatory Hajj or a vowed Hajj, the Ihram counts for the obligatory Hajj (Hajja al-Islam). This view is held by Ibn Umar, Anas, and Al-Shafi'i. The reasoning is that since the obligatory Hajj is due upon him, his Ihram fulfills the obligation, similar to an unspecified Hajj (Hajj al-Mutlaq). This principle applies equally to Umrah as it is one of the two rites (Hajj and Umrah). Furthermore, the proxy (agent) is treated the same as the principal (the one being represented); therefore, if the agent enters Ihram for a supererogatory or vowed Hajj on behalf of someone who has not performed Hajja al-Islam, it counts for that person's obligatory Hajj.