I heard Ali in the open courtyard appealing to the people, asking whoever had witnessed the Messenger of Allah ﷺ on the day of Ghadir Khumm and heard what he said to come forward. Thirteen men stood up and testified that they had heard the Messenger of Allah ﷺ say, "Whoever I am his master, Ali is his master."
حدثنا ابن نمير حدثنا عبد الملك عن أبي عبد الرحيم الكندي
سمعت عليا في الرحبة وهو ينشد الناس من شهد رسول الله ﷺ يوم غدير خم وهو يقول ما قال فقام ثلاثة عشر رجلا فشهدوا أنهم سمعوا رسول الله ﷺ وهو يقول من كنت مولاه فعلي مولاه
Its chain of transmission is daif due to the unknown status of some of its narrators. Haythami mentioned it in Majma al-Zawaid, 9/107, and said, "It contains narrators I do not recognize." This is indeed as he said.Abdul-Malik, this is how it appears in H and M, "Abdul-Malik, from Abu Abdul-Rahim Kindi." In L it appears as "Abdul-Malik bin Abu Abdul-Rahim." In Tajil, 266, it appears as "Abdul-Malik," without further lineage, "from Abdul-Kareem Kindi, and from him Abdullah bin Ahmad." Our teacher Haythami added this as a supplement, but it is not sound. I have already clarified in the biography of Abdul-Rahim that he is Abdul-Malik bin Umayr, the well-known Follower.Thus in Tajil it says "Abdul-Kareem," but the correct form is "Abu Abdul-Rahim," and it says "Abdullah bin Ahmad," but the correct form is "Abdullah Ibn Numayr." I do not know, then, on what basis Ibn Hajar concluded definitively that he is Abdul-Malik bin Umayr the Follower.He said in the biography of Abdul-Rahim, 259, "Abdul-Rahim Kindi, from Zazan bin Umar, from Ali. Abdul-Malik bin Umayr narrated from him." Our teacher Haythami added this as a supplement, but his narration in the original text of the Musnad reads "from Abdul-Malik, from Ibn Abdul-Rahim." Likewise there it also says "Zazan bin Umar," but the correct form is "Zazan Abu Umar," and it says "from Ibn Abdul-Rahim," but the correct form is "from Abu Abdul-Rahim." Then in the section on kunyas, 500, it says "Abu Abdul-Rahim Kindi," and then says nothing further, leaving what should follow his name blank. So Haythami was indeed correct that he did not recognize some of its narrators.Zazan Abu Umar Kindi Kufi, the blind, was a trustworthy Follower. In Tahdhib another view is related, that his kunya was Abu Abdullah, but the stronger view is Abu Umar, since that is how he is given the kunya in Tabaqat Ibn Saad, 6/124, and Kuna of Dulabi, 2/42. In H it says "Zazan bin Umar," which is an error.As for the text of the hadith, it is sahih, and it has come down through many routes. Munawi mentioned in his commentary on Jami Saghir, under hadith 9000, quoting Suyuti, that he said, "This is a mutawatir hadith." Its routes, or most of them, are found in Majma al-Zawaid, 9/103-109.Khumm, with the kha vowelled with damma and the meem doubled, is a valley between Makkah and Madinah near Juhfah, where there is a pool beside which the Messenger of Allah ﷺ delivered a sermon. See also 950 and 670.