EID GHADEER was first established and commemorated by the Buyid Empire around 352 Hijri, just like Moharram's Mourning Commemoration. Shia Historian Ameer Ali has written in his book "Short History of The Saracen"
"Moiz ud Dawlah (King of the Buyid Empire at that time) was cruel by nature, .He was a Shia, and it was he who established the 10th day of the Moharram as a day of Mourning in commemoration of the massacre of karbala"
Rest you can read about Buyid Empire by clicking on this link below
https://www.medievalists.net/2019/06/buyids-brothers/#:~:text=Some%20of%20the%20Shia%20festivals,on%20the%2010th%20of%20Muharram
Likewise, Sunni scholar and historian Imam ibn Atheer رحمہ اللہ writes:
وَفِيهَا فِي الثَّامِنِ عَشَرَ ذِي الْحِجَّةِ، أَمَرَ مُعِزُّ الدَّوْلَةِ بِإِظْهَارِ الزِّينَةِ فِي الْبَلَدِ، وَأُشْعِلَتِ النِّيرَانُ بِمَجْلِسِ الشُّرْطَةِ، وَأُظْهِرَ الْفَرَحُ، وَفُتِحَتِ الْأَسْوَاقُ بِاللَّيْلِ، كَمَا يُفْعَلُ لَيَالِيَ الْأَعْيَادِ فُعِلَ ذَلِكَ فَرَحًا بَعِيدِ الْغَدِيرِ، يَعْنِي غَدِيرَ خُمٍّ، وَضُرِبَتِ الدَّبَادِبُ وَالْبُوقَاتُ، وَكَانَ يَوْمًا مَشْهُودًا.
And in the year 352 Hijri, 18 Dhul Hijjah Muiz ud Dawlah ordered to beautify and decorate the city, and glowed up court's gathering with lights and and gates were opened just like the gates were opened in Eid nights, and celebrated with happiness on occasion of Eid Ghadeer khumm, and drums were beaten and trumpets were blown, these sights were memorable.
[al Kafil fi tareekh 7/246]
Another Sunni historian Imam ibn Kathir writes:
وَفِي ثَامِنَ عَشَرَ ذِي الْحِجَّةِ مِنْهَا أَمَرَ مُعِزُّ الدَّوْلَةِ بِإِظْهَارِ الزِّينَةِ بِبَغْدَادَ وَأَنْ تُفْتَحَ الْأَسْوَاقُ بِاللَّيْلِ كَمَا فِي الْأَعْيَادِ، وَأَنْ تُضْرَبَ الدَّبَادِبُ وَالْبُوقَاتُ، وَأَنْ تُشْعَلَ النِّيرَانُ بِأَبْوَابِ الْأُمَرَاءِ وَعِنْدَ الشُّرَطِ ; فَرَحًا بَعِيدِ الْغَدِيرِ - غَدِيرِ خُمٍّ - فَكَانَ وَقْتًا عَجِيبًا وَيَوْمًا مَشْهُودًا، وَبِدْعَةً ظَاهِرَةً مُنْكَرَةً.
And in the year 352 Hijri 18th Dhil Hajj Moiz ud Dawlah ordered to decorate the city and just like Eid nights he ordered to open the markets, trumpets and drums were beaten and trumpets were blown, and lightings were illuminated at the doors of governors and army, time of joy on the occasion of Eid Ghadeer was weird and full of sight and it was the day of apparent evil innovations (bidah).
[Al bidayah 10/261]
So, it is clear and evident that this festival "Eid Ghadeer" has nothing to do with Islam rather it is originated by Shia King of Buyid Dynasty and Ironically Shias were totally unaware about this Eid until Imam Jafar as Sadiq told them about it.
Shia Mohaddis Kulayni narrated from Salim that he asked Imam Jafar as Sadiq that:
هَلْ لِلْمُسْلِمِينَ عِيدٌ غَيْرَ يَوْمِ اَلْجُمُعَةِ وَ اَلْأَضْحَى وَ اَلْفِطْرِ؟
Is there any other Eid, other than Juma'a, Eid al Fitr and Eid al Adha?
Imam Jafar then answered: Yes, This Eid is included in our three Eids, also Juma'a, Salim then qsked "Do we have any other Eid"? If Prophet ﷺ ever mentioned this Eid, then this Eid would have been known by all of us specially us (Shia).
Imam Sadiq replied: This Eid (Eid Ghadeer) is greatest and full of virtues. Salim asked: What Eid is that? Imam Sadiq answered:
اَلْيَوْمُ اَلَّذِي نَصَبَ فِيهِ رَسُولُ اَللَّهِ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ أَمِيرَ اَلْمُؤْمِنِينَ عَلَيْهِ اَلسَّلاَمُ.....
This was that day when Prophet ﷺ declared Ameerul Momineen Saydna Ali as the leader of the people........
Isn't it weird that Shia knew about 2 Eids but not the Greatest one "Eid Ghadeer" as the narrator himself affirmed it and accepted it that Shias never knew about this "Eid Ghadeer" at all and Prophet صلی اللہ علیہ وسلم never told them and taught them about it.
How recklessly Shia Rafidha baffled themselves and forged hadith and virtues of Eid Ghadeer in the name of Islam during the period of Buyid Empire.
