Saad bin Abu Waqqas reported that the Prophet ﷺ said to Ali, "You are to me as Harun was to Musa, except that there is no prophet after me."
أن النبي الله ﷺ قال لعلي: أنت مني بمنزلة هارون من موسى إلا أنه لا نبي بعدي.
Tirmidhi (3730) narrated it from Mahmud bin Ghaylan, who said, Abu Ahmad Zubayri told us, Sharik told us, from Abdullah bin Muhammad bin Aqeel, from Jabir bin Abdullah, and he related the hadith. Its chain is hasan because of what has been said about Sharik, who is Ibn Abdullah Nakhai, a disputed narrator. Ibn Saad, Ajli, and others deemed him reliable, though his memory changed after he took up the post of judge in Kufa, so he would make mistakes. The likelihood is that he did not err in this particular hadith, given the abundance of corroborating reports. Imam Ahmad (14638) also narrated it through this same route.It has also been narrated from Abu Saeed Khudri, who said, the Messenger of Allah ﷺ said to Ali bin Abu Talib, "You are to me as Harun was to Musa, except that there is no prophet after me." Imam Ahmad (11272), Ibn Abu Asim in Sunnah (1382), and Bazzar in Kashf Astar (2526) all narrated it through various chains from Atiya, from Abu Saeed, who related it. Atiya is Ibn Saad Awfi, a disputed narrator. Ibn Main deemed him reliable, while Ahmad and others deemed him weak, as Haythami stated in Majmaa.On this subject there is also what has been narrated from Ibn Abbas in a lengthy hadith, which includes, "Are you not pleased to be to me as Harun was to Musa, except that you are not a prophet? It is not fitting that I should depart without you being my successor." Ahmad (3061) narrated it from Yahya bin Hammad, who said, Abu Awana told us, Abu Balj told us, Amr bin Maymun told us, saying, I was sitting with Ibn Abbas when nine men came to him and said, "O Abu Abbas, either stand and come with us, or clear this place for us, so-and-so." Ibn Abbas said, "No, I will come with you." At that time he was still sound of sight, before he went blind. They began talking, but we do not know what they said. Then he came back shaking out his garment and saying, "Shame and disgrace on them, they have attacked a man who possesses ten qualities, they have attacked a man about whom the Prophet ﷺ said, 'I will certainly send forth a man whom Allah will never disgrace...'" and he went on to mention some of the virtues of Ali, including his saying ﷺ, "Are you not pleased..."In this chain is Abu Balj, who is Yahya bin Abu Salim Fazari, a disputed narrator. Yahya bin Main and others deemed him reliable, while Bukhari said, "There is something questionable about him." Ahmad said, "He narrated a munkar hadith, I think it is this one." The most balanced assessment of him is what Ibn Hibban said in Majruhin (1195), "He was among those who erred, but his errors were not so severe as to warrant abandoning him, nor did anything come from him beyond what is inescapable for human beings, such that he would be classed among those to be entirely discarded. So I hold that his solitary narrations should not be relied upon, and he is among those concerning whom I seek Allah's guidance."I say, this hadith before us is one of those he narrated alone, for it contains material that is not corroborated, even though some of its individual statements have sahih corroborating evidence. Shaykh al-Islam said in Minhaj Sunnah (5/34–35), after citing the hadith, "It contains statements that are fabrications attributed to the Messenger of Allah ﷺ..." and he went on at length refuting some of its statements. As for Hakim (3/132–133), after citing the hadith in full through the route of Imam Ahmad, he said, "This is a hadith sahih in chain, though the two of them [Bukhari and Muslim] did not record it in this wording." So his consideration was directed at the narrators of the chain, not at the text of the hadith itself.