9th Rabi-al-Awwal 1429 A.H. - Eid-e-Zahra. Also known as Eid-e-Shuja.
This is the day of Eid for Shia Muslims and marks the end of the mourning period after the events of the Battle of Karbala. According to Ulema, this is the day when the key murderers of Imam Hussain, Umar ibn Sa'ad and Ubaidullah ibn-e-Ziyad were killed and sent to Hell. Many Muslims prepare for Eid by applying intricate designs called mehndi, or in some cultures mehandi, to different parts of the body usually each meaning different things. This event for shia Muslims is held on 9th Rabi-al-Awwal. There isn't a specific date since Muslims follow the lunar calendar.
The two-month period of Azadari (mourning) reaches its climax with the death of the 11th Imam, Imam Hassan Askari on the 8th of Rabi al-Awwal. The day that follows, according to tradition, is the greatest Eid (celebration) for the lovers of the Ahlul Bayt. Known as Eid-E-Zehra, this day honours the daughter of Muhammad as a day of great joy and happiness for the believers
One of the events which is marked on this day is the beginning of the Imamate of the 12th Imam, al-Hujjah ibn al-Hasan. His father, Imam Hasan al-Askari died on the 8th and, immediately after, his son took over the mantle of leadership.
The day also marks the first time that the 4th Imam smiled and rejoiced after the events of Kerbala in which he saw his entire family and friends killed by Ibne Ziyaad, Umar ibne Sa’d, Yazid ibne Mu’awiyah and others. It was on 9 Rabi’ul Awwal the year 67 A.H. when Mukhtar sent the head of Ubaydallah Ziyad to Imam Zainul Abedeen who was in Makkah at the time.
Muhammad himself was seen smiling and ‘celebrating’ on this day while in the presence of Imams Ali, Hasan and Husain and said, “It is on this day that Allah will destroy your enemies and the enemies of your grandfather and it is on this day when Allah will accept the actions of your Shi’a and those who love you. This is the day when the words of Allah came true where He said (in the Qur‘an): ‘So those are the houses fallen down because they were unjust.’ (27:52) And this is the day when the Pharaoh (Firawn) of the time of the Ahlul Bayt was destroyed.
[[]ezsoftech ,world-federation.org]