The Messenger of Allah ﷺ said, "Whoever I am his master, Ali is his master."
قال رسول الله ﷺ: من كنت مولاه فعلي مولاه.
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Ibn Abu Asim narrated it in Sunnah (1393), and Nasai in Kubra (8414), both through the route of Abdullah bin Dawud, from Abdul-Wahid bin Ayman, from his father, that Saad said, and then he mentioned it. Its isnad is hasan because of Abdul-Wahid bin Ayman.Ibn Majah (121), Nasai in Kubra (8343), and Ibn Abu Asim in Sunnah (1421) all narrated it through various routes from Abdul-Rahman bin Sabit, from Saad bin Abu Waqqas, who said, "I was sitting when they began disparaging Ali bin Abu Talib, so he said, 'I heard the Messenger of Allah speak of three qualities belonging to him, and if just one of them were mine, it would be dearer to me than red camels. I heard him say, "He is to me as Harun was to Musa, except that there is no prophet after me." And I heard him say, "Tomorrow I will certainly give the banner to a man who loves Allah and His Messenger, and whom Allah and His Messenger love." And I heard him say, "Whoever's master I am, Ali is his master."'"Its isnad is disconnected, because Abdul-Rahman bin Sabit did not hear directly from Saad bin Abu Waqqas. Ibn Main said this. See Marasil (p. 127).On this subject there is also what was narrated from Bara bin Azib, who said, "We were with the Messenger of Allah on a journey, and we stopped at Ghadir Khum. A call went out among us, 'Prayer in congregation.' A spot was swept clean for the Messenger of Allah under two trees, and he prayed Dhuhr. Then he took Ali's hand and said, 'Do you not know that I have more right over the believers than they have over themselves?' They said, 'Yes.' He said, 'Do you not know that I have more right over every believer than he has over himself?' They said, 'Yes.'" He said, "Then he took Ali's hand and said, 'Whoever's master I am, Ali is his master. O Allah, be an ally to whoever is his ally, and an enemy to whoever is his enemy.'" He said, then Umar met him after that and said to him, "Congratulations, son of Abu Talib. Morning and evening you have become the master of every believing man and woman."Ibn Majah (116) and Ahmad (18479) narrated it, both through the route of Hammad bin Salama, who said, Ali bin Zayd bin Jadan told us, from Adi bin Thabit, from Bara bin Azib, and he mentioned it. Its isnad is daif because of Ali bin Zayd bin Jadan, for he is considered daif by most scholars. Busiri faulted it for this reason in Misbah Zujaja.Likewise, what is narrated from Abu Tufayl, from the Prophet, that he said to Ali, "Whoever's master I am, this is his master. O Allah, be an ally to whoever is his ally, and an enemy to whoever is his enemy," is not sound. Ahmad (19302), Nasai in Khasais Ali (93), and Tahawi in Sharh Mushkil (1762) narrated it, and Ibn Hibban (6931) graded it sahih, all of them through routes from Fitr bin Khalifa, from Abu Tufayl Amir bin Wathila, who said, and then he mentioned it in a lengthy account.Fitr bin Khalifa Makhzumi, their freedman, Abu Bakr Hannat, is disputed, and he was accused of Shiism. Abu Bakr bin Ayyash, Daraqutni, and others criticized him because of his poor doctrine, and for that reason this addition is not accepted from him.Nor does the corroboration of Habib bin Abu Thabit from Abu Tufayl help, found in Ahmad (952) and Nasai in Khasais (88), for it contains Sharik bin Abdullah Qadi, who had poor memory, and there is disagreement over whether this addition should be attributed to him.However, Hakim (3/109) narrated it through the route of Abu Awana as a corroboration for it. Nasai also narrated it in Khasais (84) through another route from Zayd bin Arqam, without mentioning this addition. It therefore appears that there was confusion in the hadith of Zayd bin Arqam regarding the mention of this addition. This addition has been reported from a number of companions, yet none of them is free from being unknown, or daif, or suspected of fabrication. Ahmad likewise said, "It is a Kufan addition." Sheikh Islam bin Taymiya quoted this in his Fatawa (417/4).He said, "As for his saying, 'Whoever's master I am, Ali is his master. O Allah, be an ally to whoever is his ally...' and so on, this is not found in any of the major hadith collections except Tirmidhi, and even there it contains nothing but, 'Whoever's master I am, Ali is his master.' As for the addition, it is not part of the hadith. Ahmad was asked about it and said, 'It is a Kufan addition.' There is no doubt that these are fabrications, for several reasons.The first is that the truth does not revolve around any single specific person except the Prophet, for if it were otherwise it would be obligatory to follow him in everything he said. Yet it is known that the companions and his own followers disputed with Ali on certain matters, and the textual evidence was found to support those who disputed with him, as in the case of a woman whose husband dies while she is pregnant.And his saying, 'O Allah, grant victory to whoever supports him...' and so on, contradicts what actually happened. Some people fought alongside him on the day of Siffin yet were not granted victory, while others did not fight yet were not abandoned, such as Saad, who conquered Iraq without fighting alongside him. Likewise, the companions of Muawiya and Banu Umaya, who fought against him, went on to conquer many lands of the disbelievers, and Allah granted them victory.Likewise, his saying, 'O Allah, be an ally to whoever is his ally, and an enemy to whoever is his enemy,' contradicts the very foundation of Islam. For the Quran has made clear that the believers are brothers despite their fighting and their transgression against one another. As for his saying, 'Whoever's master I am, Ali is his master,' some scholars of hadith criticized it, such as Bukhari and others, while some graded it hasan. If he did say it, he did not mean by it a mastery exclusive to Ali, but rather a shared mastery, the mastery of faith belonging to all believers. Alliance is the opposite of enmity, and there is no doubt that it is obligatory to ally with the believers over others. In this there is a refutation of the Nawasib." End of quote.What Sheikh Islam bin Taymiya said is undoubtedly true, and those who went on to grade it sahih did not take into account this aspect that Sheikh Islam bin Taymiya pointed out. Moreover, the soundness of an isnad does not necessitate the soundness of the text, given the presence of irregularity and other such issues. This is something well known among the scholars of hadith. And Allah grants success.