The ninth day of Dhul Hijjah is the day of Arafah.
It is the day when Hajj pilgrims stand on the plain of ‘Arafat’ (a flat wide desert about 22 km south east of Mecca) to pray. Arafat literally means knowledge and science.
1- Arafat represents the beginning of man’s creation, our forefather Hazrat-e Adam. It was the Devil (Shaytan) who misled our forefather and caused the downfall of Hazrat-e Adam (AS) and Haw’a (SA). For years, they were separated from each other having descended at different places. It was in ‘Arafat’ that they met again. It was in a small rocky hill of Jabal Al-Rahma (Mount of Mercy) in the center of ‘Arafat’ that their sins were forgiven by Allah (SWT). The devotional aspects of the gathering at Arafat is a ‘devotional act meant to bring to mind the ultimate gathering on Resurrection Day, when every soul will await God’s judgment.’
2- In addition, it recalls the last public act of the Holy Prophet (PBUH) when, during his ‘Pilgrimage of Farewell,’ he went up Mount Arafat and delivered his historical speech.
3- Imam Hussain (A.S), the Third Infallible Imam, made the supplication, Arafah Dua, one of the most famous in Shia annals, one year during the pilgrimage to Mecca on the Day of Arafah (the ninth of Dhul Hijjah), and it has been recited by Shia Muslims ever since. On that day pilgrims pass the time at Mount Arafat occupying themselves with prayer, reciting the Holy Quran, invocations and supplications. The spirit of the day is well represented in the Imam’s prayer. The Dua of Imam Hussain (A.S) on the route to the historical event of Karbala for the Day of Arafah is very famous for its sublime words and the inspiration they motivate.
The Martyrdom Anniversary of Hazrat Muslim Ibn Aqeel
The ninth day of Dhul Hijjah, is also the martyrdom anniversary of Hazrat Muslim Ibn Aqeel (AS). Hazrat Muslim ibn Aqeel (AS) was the cousin of the third infallible Imam, Hazrat Hussain ibn Ali (A.S), and was the son of Aqeel ibn Abu Talib (A.S). Muslim ibn Aqeel (AS) was sent ahead by Imam Hussain (A.S.) as his envoy to Kufa to see if the people could be trusted to be loyal. The people of Kufa swore allegiance to him and he sent word back to Imam Hussain (A.S.) saying that the people of Kufa were loyal to him. But Hazrat Muslim ibn Aqeel (AS) was brutally murdered by the governor of Kufa, Ibn Ziyad on the ninth day of Dhul Hijjah 60 A.H.
Source: en.shafaqna.com