To begin with we will quote a tradition whereby Ali ibn Abi Talib makes direct reference to this event. The tradition is deemed authentic and is in the Musnad of Ahmad.
“Abd al-Rahman Ibn Abu Laylah said: I witnessed ‘Ali administering an oath to the people in the plain of Rahbah. ‘Ali said: “I adjure those of you in the name of Allah who heard the Messenger of Allah on the day of Ghadir saying `’Ali is the Mawla of whom I am Mawla’ to stand up and to testify. He who was not an eyewitness doesn’t need to stand up.”Thereupon twelve (12) such companions who had participated in the Battle of Badr stood up. The occasion is still fresh in my memory.
Reference: [Musnad Ahmad Ibn Hanbal, v1, p119, see also v5, p366]
As we can see above, Ali ibn Abi Talib was fully cognisant and remembered what occurred on the day of Ghadeer, and placed so much emphasis on it he asked others in the name of Allah to stand up and testify that they had witnessed him say it. Now, one may argue that the above hadith does not explicitly prove the shia position or prove how Ali ibn Abi Talib interpreted it. This is true when the hadith is taken alone, but what it does prove is that he knew full well what occurred on the day , he remembered it well, and he placed great emphasis on it as demonstrated by asking others to swear by it.
Now read the following tradition from Musnad Ahmad:
Rabah bin al-Harith said: ‘A group of men passed by Ali in Rahba and they said: ‘Peace be upon you our master (Maula). ‘He (Ali) said: how can I be your master (Maula) and you are Arab?’ They replied: ‘We heard Allah’s Apostle (pbuh) state on the day of Ghadir: ‘Of whomsoever I am his master (Maula) then this (Ali) is his master (Maula)’. Rabah said: ‘When they left, I followed them and asked (people): ‘Who are they?’ They answered: ‘They are group from Ansar and Abu Ayub al-Ansari is among them”.
Reference:[Musnad Ahmad, Volume 38 page 541:] Shu’aib al-Arnaoot said: ‘The chain is Sahih’
The above tradition is very revealing. One interpretation of the above – and a very erroneous one is to suggest Ali ibn Abi Talib forgot what happened at Ghadir and was confused as to why he was calling them his Mawla, which is not a tenable one considering what has been established. Now that we have established from the first tradition in Musnad Ahmad that Ali ibn abi Talib knew full well what Mawla meant , and remembered the day of Ghadir and even got others to swear by it, we then see him make a very peculiar statement. Senior companions, such as Abu Ayub Al-Ansari and those from the Ansar [and it is significant it is these particular members and this point will be expanded on] called him their Mawla.
Secondly, some people try very hard to claim the dominant use of Mawla means friend, or beloved, and that very few people interpret it as ‘master’. However here we see Ali ibn Abi Talib himself in an authentic sunni hadith seems to interpret it as master to begin with.
Furthermore, one can see Ali ibn Abi Talib using a rhetorical and very intelligent manner of questioning. No-one can claim that Ali ibn Abi Talib forgot Ghadir, nor can anyone claim that senior members of the Sahaba were confused by Ali who thought they called him his master. Rather, what Ali ibn Abi Talib was doing here was asking a question so they they could affirm why they regarded him as their master. He was trying to test their resolve and insight by asking this. By making it clear they were free men [Arab] he wanted to ask them in which way he was their master.
Furthermore, the inclusion of Abu Ayub Al-Ansari is an important one, considering him and a number of the Ansaar are regarded by shia’s as those who returned to Ali ibn Abi Talib and opposed the appointment of the first Caliph. We also find in Tarikh-At-Tabari reports whereby members of the Ansaar advocate on behalf of Ali ibn Abi Talib:
We do not deny the merits of those you have mentioned. Indeed there is among you a person with whom if he seeks authority, none will dispute [i.e. Ali]‘.
Reference: Tarikh, by al Yaqubi, Volume 2 page 113-114, quoted from History of Tabari, Volume 9 English translation
Just to note, Abu Bakr, Umar, and Abu Ubaydah were already present at Saqifah when the scuffle was taking place. The greatest man on that list according to sunni’s by consensus [as Uthman was not mentioned] was Ali ibn Abi Talib [as]. It could only have been him the was meant, even by logic of our sunni brothers/sisters in islam. This is evident given he was not present, and they had said that one of the men in the list they would not have disputed and if they wanted authority , they would not dispute it.
“Ibn Humayd-Jarir – Abu Ma’shar Ziyad b. Mughzrahl-Kulayb-Abu Ayyub-Ibrahim- “The Ansar gathered in a roofed building (sagifah)12s9 of the Banu Sa’idah to render their oath of allegiance to Sa’d b. Ubadah. This news reached Abu Bakr, so he came to them with’Umar and Abu’Ubaydah b. al-Jarrah, asking [them] why [they had gathered]. They replied, “Let us have a ruler (amir) from us and another from you.” Abu Bakr said, “The rulers will be from us, and the viziers from you.” Abu Bakr then added, “I am pleased [to offer] you one of these two men: ‘Umar or Abu ‘Ubaydah. Some people came to the Prophet asking him to send a trustworthy man with them. The Messenger of God said that he would send a truly trustworthy man with them, and he sent Abu ‘Ubaydah b. al-Jarrah. I am pleased [to offer] you Abu ‘Ubaydah.” ‘Umar stood up saying, “Who among you would be agreeable to leave Abu Bakr whom the Prophet gave precedence? 11290 and he gave him the oath of allegiance. The people followed [‘Umar]. The Ansar said, or some of them said, “We will not give the oath of allegiance [to anyone] except ‘Ali.”
Reference: History of Tabari.