What is the reason for celebrations on the 9th of Rabi-al-Awwal and when did this tradition start…

Al-Sayed ibn Tawoos writes in the book, ‘Zawaa’id al-Fawaa’id’ that Ibn Abi Alaa Al-Hamadani al-Waasiti and Yahya ibn Mohammad bin Huwaij Al-Baghdadi said:
We were quarreling about ibn Al-Khattab (Omar) and we became uncertain about him, so we travelled to Ahmad bin Isaac al-Qummi (Imam Hassan Al-Askari’s(as) companion) in Qum.
We knocked on his door, and a young Iraqi girl opened. We asked to see Ahmad bin Isaac, to which she replied,
“He is busy with his festival (eid), for it is a day of celebration”
I said, “Praise be to Allah! The Shia festivals are four; Al-Fitr, Al-Ad’ha, Al-Ghadeer and Jomaa”.
She said, “Ahmad bin Isaac narrates from his master Abul Hassan, Ali bin Mohammad Al-Askari(as), that this day is a day of Eid, and it is in fact the most blessed of Eid’s for Ahlul Bayt(as) and their followers”
We then told her to inform him of our presence and seek permission for us to enter.
Ahmad bin Isaac came to greet us dressed in a loincloth and perfumed with musk. We criticized his action, to which he replied, “Don’t worry, for I have just done ritual ghusl for Day of Eid”. We said, “Is it a day of Eid?” He replied in the affirmative. It was the 9th of Rabi-al-Awwal.
He invited us in and when we were seated he said, “I went to visit my Master Abu al-Hassan(as) in Samarra on the same day as this, 9th Rabi-al-Awwal. He instructed all his servants to wear new clothes, and he was burning scented wood an incense pot.
I said to him, “May our fathers and mothers be a sacrifice for you! O son of the Messenger of Allah! has a day of celebration been renewed for Ahlul Bayt(as) today?”
He said, “Is there a more sacred day for Ahlul bayt(as) than this day, 9th Rabi-Al-Awwal?
My father narrated to me that, on this day Huthaifa bin Al-Yamani went to visit my grandfather, the Messenger of Allah (saww). Huthaifa said, “I saw Ameerul Momineen(as) and his children eating with the Prophet (saww). The Prophet (saww) was looking at their faces, smiling and saying to Al-Hassan(as) and Al-Hussain(as), ‘Eat! Eat! enjoy the blessings and felicities of this day!, for it is the day that Allah(swt) will destroy His enemy, and the enemy of your grandfather;
It is the day Allah(swt) will accept the deeds of your followers and lovers;
It is the day the pharaoh of Ahlulbayt(as) will be annihilated, their oppressor and the usurper of their rights;
It is the day Allah(swt) will proceed to what they have done of deeds, and He will render them as scattered floating dust’.
I said, “O Messenger of Allah(saww)! Is there from amongst your nation and companions, he who will violate these sanctities?”
The Prophet said, “Yes Huthaifa, A tyrant from amongst the hypocrites. He will rule over them in a swaggering dictatorial manner and use deceit amongst my Ummah. He will bar the people from following the path of Allah(swt) and distort His Book and change my Sunnah. He will usurp my children’s inheritance and appoint himself as an authority. He will have the audacity to attack his Imam after me and will seize the people’s wealth in a way not prescribed and will squander it disobediently.
He will belie me and belie my brother and vizier. He will enviously appropriate my daughter’s rights. She will invoke God, and He will answer her prayers on a day like this”.
Huthaifa said, “O Messenger of Allah(saww), invoke Allah(swt) to destroy him in your life time”
The Messenger of Allah(saww) said, “Huthaifa, I loathe challenging the decree of Allah(swt), although I have asked Allah(swt) to give virtue to the day on which he perishes over all days, so that it becomes a practice observed by my loved ones and followers of my Ahlulbayt(as). Whereupon Allah, the Exalted, revealed to me saying,
“O Mohammad(saww)! You and your AhlulBayt(as) will be afflicted with worldly calamities and adversities, also the oppression of the hypocrites and usurpers from amongst My servants whom you counseled, only to be betrayed by them. You were sincere towards them, yet they deceived you; you showed them kindness and they drove you away.
I will, by My power and might, open 1000 doors of hellfire from the lowest pits of hell and cast therein those who usurp the rights of your brother Ali(as). I will make an example of that hypocrite on the Day of Judgment, and like the pharaohs of all the prophets and the enemies of the religion, I will gather them and their companions in the Hellfire and therein they will abide eternally.
O Mohammad(saww)! Your vicegerent and companion will suffer much affliction from this pharaoh and usurper who will have the audacity to alter My words. He will associate with me a partner and avert people from My path. He will erect himself as the Golden Cow of your ummah and disbelieve in me. I have commanded My angels in the seven heavens, your Shia and adorers to celebrate the day I annihilated him on. And I have ordered My angels to praise Me and seek forgiveness for your Shia and adorers.
O Mohammad(saww)! And I have asked the Honorable Scribes (Al-Kiraam Al-Kaatibeen) to lift the Pen on that day and not to write any of my creations errors in honor of you and your vicegerent.
O Mohammad(saww)! I have made that day a day of eid for you and your AhlulBayt(as) and their followers and Shia. I vow by My Glory and Magnificence that I will favor the one who celebrates that day with the rewards of the (angels) surrounding (the throne), and I will give him permission to intercede for close kin, and I will increase his wealth. And I will free, every year, on that day, thousands of your Shia, adorers and followers from the fires of hell and recompense their striving, forgive their sins and accept their deeds.
Huthaifa said, “The Prophet(saww) then stood and entered the house of Um Salama, and I left with no doubts in my mind about the second (Umar). And I saw him after the death of the Prophet facilitate evil, disbelieve and apostatize, embark on the seat of authority (caliphate), manipulate the Quran, burn the House of Revelation (Fatima’s), innovate in the sunnah, reject the testimony of Ameerul Momineen(as), belie Fatima(sa) – the daughter of the Messenger, usurp Fadak from her, satisfy the Jews, Christians and Majoos, and annoyed the apple of the Mustafa’s eye – never ever satisfying her. He changed the traditions and lay the groundwork for the killing of Ameerul Momineen(as). He manifested injustice, prohibited what Allah(swt) had made permissible and made permissible what Allah had prohibited, and oppressively and offensively ascended the pulpit of the Prophet(saww), slandered Ameerul Momineen(as) and opposed and nullified his opinion”.
Huthaifa said, “Allah answered the prayers of my master (Imam Ali(as)) in relation to this hypocrite (Umar), and he was killed at the hands of (Abu Lulu) he who killed him, may Allah(swt) have mercy on his soul”.
Huthaifa continues, “I visited Ameerul Momineen(as) to pass on my felicities when that munafiq (Umar) was killed and he said, ‘O Huthaifa, do you remember that day when you visited the Messenger of Allah(saww) when his grandchildren and I were eating with him and he pointed out to you the excellence of this day’”
I said, “Yes, dear brother of the Messenger of Allah(saww)”
He then said, “By Allah(swt)! Today is that day – the day Allah(swt) satisfied the children of the Messenger, and I am aware of many names for this day”
I asked, “O Prince of the Faithful, I would love to hear from you the names for this day – 9th rabi al-awwal”
The Imam said, “It is the day of respite, the day of relief from distress and agony, it is a second Ghadir, it is the removal of burden, it is the day of favoritism and the lifting of the pen, the day of hady (gift) and aqiqa, the day of blessing, the day of vengeance. It is the Great Eid of Allah and the day supplications are answered, the day of great standing, the day of turning back, the day of provision, the day erected walls are demolished, the day of regret for the oppressors, the day of victory for the Shia, the day worries are expelled, the day of triumph, the day of submission the day of power, the day of pardon, the day of jubilance for the Shia, the day of reflection, the day of great charity, the second Fitr, the day of Allah’s(swt) path, the day of contentment, the day of Eid for AhlulBayt(as), the day of victory for Bani Israel, the day Allah(swt) accepted the deeds of the Shia, the day of providing sadaqah, the day of asking for an increase, the day the hypocrite is killed, the day of reckoning, the day of AhlulBayt’s(as) cheerfulness, the day that is witnessed, the day the oppressor will bite his hands, the day misguidance will be demolished, the day of accomplishment, the day of witnessing, the day of pardon for the faithful, the day of Al Mustataab, the day the authority of the munafiq departs, the day of settlement, the day the faithful relaxes, the day of Mubahila, the day of boasting, the day of thankfulness, the day victory for the oppressed, the day of visitation, the day of love, the day innovations are exposed, the day of piety, the day of exhortation, the day of worship, the day of Islam…”
Huthaifa said, “I got up and left Ameerul Momineen(aS), saying to myself, ‘If I do not succeed in achieving rewards for deeds other than those rewarded for this day, I would be satisfied”
Mohammad bin Abi Al-alaa and Yahya bin jareeh said, “Each of us got up and kissed the forehead of Isaac and said, ‘Praised be the Lord for not taking our souls before honouring us with this blessed day – and we left his place and celebrated that day, and it is the Eid of the Shia”

Source: Bihaar Al-Anwaar, Volume 31, Page 120-129 (See Image)

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