“Iblagh” (“delivering”) verse undoubtedly has been descended in Ghadir.

In Ghadir, one of the controversial discussions between Shia and Sunni commentators is the discussion about the cause of the revelation (Sha’n-e-Nozoul) of verse 67 of chapter Ma’idah saying: “O Messenger! Deliver what has been revealed to you from your Lord. And if you do not, then you will not have delivered His message. And Allah will protect you from the people. Surely Allah will not guide the unbelieving people.”  

Shias unanimously believe that this verse has been descended (revealed) on the Day of Ghadir Khum and in Imam Ali’s honor, and the purpose of it is to express the Imamate and succession of Imam Ali (P.B.U.H.). After this verse was revealed, the Holy Prophet Mohammad (P.B.U.H.) ordered all people to gather in Ghadir Khum and expressed the very famous speech “Whoever I am his/her Mola, then he (Ali) is his/her Mola”.

By studying the sources of Sunnis, we realize that in various books they have written, many narrations are found saying outspokenly: The above-mentioned verse has been descended about Imam Ali (P.B.U.H.). A huge number of Sahabah (the companions of the Holy Prophet (P.B.U.H.)) have quoted these narrations, including “Zaid-ibn-Argham”, “Abu-Sa’eed Khudri”, “Ibn-e-Abbas”, “Jaber-ibn-Abdullah Ansari”, “Abu-Horayrah”, “Bara’-ibn-Azeb”, “Huzayfah”, “Amer-ibne-Layli-ibne-Zamrah” and “Ibn-e-Mas’oud”. They have said that the above-mentioned verse has been descended on Imam Ali (P.B.U.H.) and the events of Ghadir Day. 

Some of the above-mentioned narrations, like the narration of “Zaid-ibn-Argham”, have been quoted in one way. The narration of “Abu-Sa’eed Khudri” and the narration of “Ibn-e-Abbas” have been quoted in 11 ways. The narration of “Bara’-ibn-Azeb” has also been quoted by 3 ways.

The scholars who have mentioned this narration in their books outspokenly are many numerous. For instance, we point to some of them:

1. “Hafez Abu-Na’eem Esfahani” in the book “Ma Nozzela Men al-Qur’an Fi Ali” (quoted from Khasa’es, p. 29).
2. “Abu-l-Hasan Vahedi Neyshabouri” in the book “Asbab-u-Nnuzoul” p. 150
3. “Hafez Abu-Sa’eed Sejestani” in the book “al-Welayah” (quoted from the book “Tara’ef”).
4. “Ibn-e-Asaker Shafe's” (quoted from al-Durar-ul-Manthour, vol. 2, p. 298) and Fakhr-e-Razi in his Kabir (great) Tafsir (interpretation), vol. 3, p. 636
5. “Abu-Ishaq Hamawayni” in the book “Fara’ed-u-Ssemtain”
6. “Ibn-e-Sabbagh Maleki” in the book “Fusoul-ul-Mohhimmah”, p. 27
7. “Jalal-u-Din Suyouti” in the book “al-Ddurar-ul-Mansour”, vol. 2, p. 298
8. “Ghazi Shawkani” in the book “Fath-ul-Qadir”, vol. 3, p. 57
9. “Shahab-u-Din Alousi Shafe's” in Rouh-ul-Ma’ani, vol. 6, p. 172
10. “Sheikh Soleiman Qondouzi Hanafi” in the book “Yanabi’-ul-Mawaddah”, p. 120
11. “Badr-u-Ddin Hanafi” in the book “Umdat-ul-Qari Fi Sharh-e Sahih-el-Bokhari”, vol. 8, p. 584
12. “Sheikh Mohammad Abduh Mesri” in the book “Tafsir-al-Menar”, vol. 6, p. 463
13. “Hafiz-ibn-Mardawaih” (died in 416 A.H.) quoted from Suyouti in the book “Durar-ul-Mansour”

And a large number of other scholars have quoted the same cause of the revelation for the above-mentioned verse.

Of course, it does not mean that the above-mentioned scholars and commentators have accepted that this verse has been descended from Imam Ali (P.B.U.H.). But it means that they have quoted in their books the narrations concerning this issue. However, after quoting the narrations, they have refused to accept it due to fear of the particular circumstances of their environment, or due to incorrect prejudices that prevent them from making sound judgments in such matters.

Reference: https://btid.org/fa/news/56689