Sharif Murtadha in his book Al-Shafi:
Abbas bin Abd al-Muttalib spoke to Amir Al-Muminin (Ali bin Abi Talib) during the illness of the Prophet (peace be upon him), so that he asks the Prophet, who will be in charge of affairs after him, and that if it is for us (Ahl al-Bayt) he should reveal it; and if it is for some other people, he entrust it to us. The leader of the faithful (Ali) said, we went to the Messenger of Allah when his illness became serious and we said O Messenger of Allah, choose a successor for us, He said. “No, I fear that you will be divided regarding him, as the children of Israel became divided over Harun, but if Allah knows any goodness in you, He will choose for you (a leader).
Further, another version of the hadith which supports Imam Ali's (as) belief in Shura during the process:
“No, we did go to the Prophet of Allah and said,” Appoint (for us a leader), and he said” No, I fear that you will be divided on his affairs, as Harun, but if Allah finds any good in your hearts, he will choose for you’ They requested him to point to someone, but he did not . They then said to him,” If we lost you, we will not lose giving our oath of allegiance to Hassan. He said, “I do not command, nor prevent you, you can discern better”.
Murtada: Al-Shafi, vol. 3 p. 295, Tathbit Dala'il al-Nubuwwah, vol.1 p. 212
This was during the process of the Caliphate of Imam Hassan (as) when the Muslims came to him after the strike of Abdul Rahman bin Muljan on him, and requested him to appoint his son Hassan after him (as the leader).
We even have similar narrations in our books stating:
"They said to caliph Ali: Will you not appoint a successor? he said: No, but I leave you as the apostle of Allah left you. "
-Haythami in Mujama’a al Zawa’ed; "Sahih"
"They said to Ali: Will you not appoint a successor? He said: The Prophet PBUH did not appoint a successor so that I may do so, If Allah wishes that something good happens to you then he will make you all gather around the best (Man) amongst you just like he made them gather around the best Man (i.e Abu bakr) after their prophet PBUH."
-Al haythami in Mujama’a al Zawa’ed; "Sahih"
In fact, Sharif Murtadha goes even further and states that the event of Ghadir itself is unclear about succession:
Narrated by Ibn Abbas:
`Ali bin Abi Talib came out of the house of the Prophet (S.A.W.) during his fatal ailment. The people asked (`Ali), "O Abu Hasan! How is the health of Allah's Messenger (S.A.W.) this morning?" `Ali said, "This morning he is better, with the grace of Allah." Al-`Abbas held `Ali by the hand and said, "Don't you see him (about to die)? By Allah, within three days you will be the slave of the stick (i.e., under the command of another ruler). By Allah, I think that Allah's Messenger (S.A.W.) will die from his present ailment, for I know the signs of death on the faces of the offspring of `Abdul Muttalib. So let us go to Allah's Messenger (S.A.W.) to ask him who will take over the Caliphate. If the authority is given to us, we will know it, and if it is given to somebody else we will request him to recommend us to him. " `Ali said, "By Allah! If we ask Allah's Messenger (S.A.W) for the rulership and he refuses, then the people will never give it to us. Besides, I will never ask Allah's Messenger (S.A.W.) for it."-Bukhari
But wait, I thought Imam Ali (as) was already the appointed successor at Ghadeer? Why is he asking the Prophet (S.A.W.) for rulership if the Prophet (S.A.W.) had already appointed him?
“We do not claim absolute knowledge in the text
(above), neither for ourselves nor against our opponents, and we do not know of
any of our people who claim that." (Murtada: Al-Shafi, vol 2 p. 128)
Another proof regarding Imam Ali's (as) acceptance of the Shura and the right of the Ummah to elect its leader:
“What is obligatory in the laws of Allah and Islam is that the Muslims, of if their leader dies or is killed, they should not perform any act nor innovate something, nor move in order to do something new, unless they choose for themselves a chaste leader, who is learned, scrupulous, and well-versed in the legal and traditional matters.”
Even in the Sermon of Shaqshaqiya, Imam Ali (as) does describe himself the most deserving of the caliphate based on his closeness to the Prophet (pbuh), but never does he (as) point to any existence of any wasiyyah from the Prophet (pbuh) or even mentions the event of Ghadir in regard to the Prophet (pbuh) specifying him as the successor. If the event of Ghadir was so important which the Shia's claim, Imam Ali (as) would have referred to it in clear terms. In fact, here's a narration from Al-Hasan ibn Al-Hasan bin Ali bin Abi Talib (as) regarding this:
Another proof regarding Imam Ali's (as) acceptance of the Shura and the right of the Ummah to elect its leader:
“What is obligatory in the laws of Allah and Islam is that the Muslims, of if their leader dies or is killed, they should not perform any act nor innovate something, nor move in order to do something new, unless they choose for themselves a chaste leader, who is learned, scrupulous, and well-versed in the legal and traditional matters.”
-Majlisi: Bihar al-Anwar, vol. 8 p. 555
"Hadn't the messenger of Allah (pbuh) said, "Whoever's mawla I am, then Ali is his mawla"? He said, "Yes, but by Allah, the Messenger did not intend by that the position of leadership and power. If he wanted that, he would have said it outright. Allah's messenger (PBUH) was more straightforward and the best adviser to the Muslims, if he wanted to say this, he would have said, "This is the one who will administer your affairs and look after you after me, so listen to him and obey." By Allah, if Allah and His messenger had picked Ali, Allah would have facilitated his position for him. If Ali did not step up to that position, Ali would have been the first one to disobey Allah and His messenger."
-Ibn Katheer in al-Bidayah wal Nihayah 9/178 and al-Haythami in al-Sawa’eq al-Muhriqa p346:
al-Mezzi said in Tahtheeb al-Kamal 6/88: “And this is from the highest and most authentic Isnads."
“Did not the Messenger of Allah say to Ali: ‘If i am Mawla of someone, Ali is his Mawla?’” He (Al Hasan) replied, “By Allah, if he meant by that Amirate and rulership, he would have been more explicit to you in expressing that, just as he was explicit to you about the Salah, Zakat and Hajj to the House. He would have said to you, ‘Oh people! This is your leader after me.’ The Messenger of Allah gave the best good counsel to the people (i.e. clear in meaning). “If it is like what you say, that Ali was chosen for this after the Prophet (pbuh), then he would be the most flawed from all the people, because he didn't do as the Prophet (pbuh) commanded.”
(Source: Al-Tabaqat Al-Kubra, Volume 5) Similar is present in Ibn `Asakir (volume 4, page 166) and (awaasim min qawaasim page 115).
Ibn Sa’d:
In a discussion between a Rafidhi and supposedly Hasan ibn Al-Hasan:
فقال له الرافضي ألم يقل رسول الله عليه السلام لعلي من كنت مولاه فعلي مولاه؟ فقال أما والله أن لو يعني بذلك الامرة والسلطان لأفصح لهم بذلك كما أفصح لهم بالصلاة والزكاة وصيام رمضان وحج البيت ولقال لهم أيها الناس هذا وليكم من بعدي
The Rafidhi said: ‘Did not the Messenger of Allah (saw) say to Alee (a.s): “Whomever I am his Master (Mawla) then Alee is his Master (Mawla)?”‘ He said: ‘By Allah (swt), if he meant by that the leadership, then he should have clarified that, like he clarified the issue of Salat and Zakat and fasting in Ramadan and the Hajj of the House. He should have rather said: “O people this is your Master (Wali) after me”‘.
Source: Tabaqat Ibn Sa’d. Vol. 7, Pg. # 314.
“Did not the Messenger of Allah say to Ali: ‘If i am Mawla of someone, Ali is his Mawla?’” He (Al Hasan) replied, “By Allah, if he meant by that Amirate and rulership, he would have been more explicit to you in expressing that, just as he was explicit to you about the Salah, Zakat and Hajj to the House. He would have said to you, ‘Oh people! This is your leader after me.’ The Messenger of Allah gave the best good counsel to the people (i.e. clear in meaning). “If it is like what you say, that Ali was chosen for this after the Prophet (pbuh), then he would be the most flawed from all the people, because he didn't do as the Prophet (pbuh) commanded.”
(Source: Al-Tabaqat Al-Kubra, Volume 5) Similar is present in Ibn `Asakir (volume 4, page 166) and (awaasim min qawaasim page 115).
Ibn Sa’d:
In a discussion between a Rafidhi and supposedly Hasan ibn Al-Hasan:
فقال له الرافضي ألم يقل رسول الله عليه السلام لعلي من كنت مولاه فعلي مولاه؟ فقال أما والله أن لو يعني بذلك الامرة والسلطان لأفصح لهم بذلك كما أفصح لهم بالصلاة والزكاة وصيام رمضان وحج البيت ولقال لهم أيها الناس هذا وليكم من بعدي
The Rafidhi said: ‘Did not the Messenger of Allah (saw) say to Alee (a.s): “Whomever I am his Master (Mawla) then Alee is his Master (Mawla)?”‘ He said: ‘By Allah (swt), if he meant by that the leadership, then he should have clarified that, like he clarified the issue of Salat and Zakat and fasting in Ramadan and the Hajj of the House. He should have rather said: “O people this is your Master (Wali) after me”‘.
Source: Tabaqat Ibn Sa’d. Vol. 7, Pg. # 314.