Hajj, the pilgrimage to Makkah, is one of the five pillars of Islam and was made obligatory on Muslims during the time of Prophet Muhammad (PBUH). The command to perform Hajj was revealed in the Quran, but the exact timing of when it became compulsory is significant in Islamic history.

The obligation of Hajj was established in the 9th Hijri year. This was the year when the Prophet (PBUH) returned to Makkah with a large number of Muslims in what is known as the "Farewell Pilgrimage" or Hajj al-Wada.

This year is important because it marks the first time the Muslims performed Hajj on a large scale after the conquest of Makkah. The rituals were clearly established, and the pilgrimage became a mandatory religious duty for all capable Muslims.

Understanding the Hijri year when Hajj was made compulsory helps students and scholars place Islamic practices in historical context. It is a common question in Islamic MCQs and religious education.