O Ali, you are a leader in this world and a leader in the Hereafter

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) looked at Sayyiduna Ali (may Allah be pleased with him) and said: "O Ali! You are a leader in this world and a leader in the Hereafter. Your beloved is my beloved, and my beloved is the beloved of Allah; your enemy is my enemy, and my enemy is the enemy of Allah; and woe to the one who hates you after me."
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), and Abu al-Azhar is trustworthy by consensus; and when a trustworthy narrator is alone in narrating a hadith, that narration is sahih according to them (the hadith scholars).

It is narrated from Ahmad bin Yahya al-Hulwani that when Abu al-Azhar returned from San'a and mentioned this hadith before the people of Baghdad, Yahya bin Ma'in rejected it. Then, when the day of his gathering came, at the end of the gathering he asked: "Where is that liar from Naysabur who narrates this hadith on the authority of Abd al-Razzaq?" Abu al-Azhar stood up and said: "Here I am." Yahya bin Ma'in laughed at his words and at the way he stood up in the gathering; then he called him close and said: "How did Abd al-Razzaq narrate this hadith to you alone, when he did not tell it to anyone other than you?" He replied: "O Abu Zakariyya! Know that when I reached San'a, Abd al-Razzaq was in a distant village of his. I set out towards him while I was ill. When I reached him, he asked me about the affairs of Khurasan, and I told him about them. I wrote hadith from him and then returned with him to San'a. When I was bidding him farewell, he said to me: Your right over me has become due, so I will narrate to you a hadith that no one besides you has heard from me. Then, by Allah, he narrated this hadith to me in these very words." So Yahya bin Ma'in affirmed his truthfulness and apologised to him.

It is narrated from Sayyiduna Abu Dharr (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said to Sayyiduna Ali bin Abi Talib (may Allah be pleased with him): "Whoever obeys me has obeyed Allah, and whoever disobeys me has disobeyed Allah; and whoever obeys you has obeyed me, and whoever disobeys you has disobeyed me."
The chain of narration of this hadith is sahih (authentic), but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Zayd bin Arqam (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever wishes to live as I live, die as I die, and dwell in the Garden of Eternity which my Lord has promised me, let him take Ali bin Abi Talib as his wali (friend and guardian), for he will never take you out of guidance, nor will he ever lead you into misguidance."
The chain of narration of this hadith is sahih (authentic), but the two Shaykhs (Bukhari and Muslim) did not record it.