Scholarly consensus (ijmaa‘) as binding proof and the first consensus that occurred in Islam
Question

I would like to know what was the first consensus (ijmaa‘) that happened in the history of Islam, and what is the importance of consensus?
Praise be to Allah.Firstly:
Consensus (ijmaa‘) is one of the important sources of legislation that must be followed.
There are several definitions of consensus (ijmaa‘); the favoured view is that of as-Subki (may Allah have mercy on him), who defined it as follows: It is when there is unanimous agreement among the scholars of the ummah after the death of Muhammad (blessings and peace of Allah be upon him), during any era, on some particular matter.
End quote from Jam‘ al-Jaami‘, annotated by Wali ad-Deen al-‘Iraaqi, which is known also known as al-Ghayth al-Haami‘, p. 485
There is a great deal of definitive evidence from the Qur’an and Sunnah for the fact that consensus constitutes binding proof. We have explained some of it previously in the answer to question no. 201682 .
For example, Allah, may He be exalted, says (interpretation of the meaning):
“And whoever opposes the Messenger after guidance has become clear to him and follows other than the way of the believers - We will give him what he has taken and drive him into Hell, and evil it is as a destination”
[an-Nisa’ 4:115].
Ibn Hazm (may Allah have mercy on him) said: Whoever goes against it – that is, consensus – after coming to know of it, or after proof has been established on the basis of consensus, is deserving of the warning mentioned in the verse.
End quote from Maraatib al-Ijmaa‘ by Ibn Hazm, p. 7.
Al-Qaadi Abu Ya‘la (may Allah have mercy on him) said: Consensus constitutes binding proof with which one should comply and it is haraam to go against it; it is not possible for the ummah to agree on error.
End quote from al-‘Uddah fi Usool al-Fiqh (4/1058).
Secondly:
We have not come across anyone who mentioned the first consensus that occurred in Islam, or the first one to narrate such a thing.
We have stated above that consensus is when the scholars agree on a particular issue after the death of the Prophet (blessings and peace of Allah be upon him).
However, during his lifetime (blessings and peace of Allah be upon him), consensus did not constitute proof.
Al-Aamidi (may Allah have mercy on him) said: The consensus of those who were alive at the time of revelation did not constitute proof at the time of revelation, according to consensus; rather consensus became binding proof after the death of the Prophet (blessings and peace of Allah be upon him).
End quote from al-Ahkaam by al-Aamidi (1/109).
Based on that, it may be said that the first consensus that occurred after the death of the Prophet (blessings and peace of Allah be upon him) was the consensus of the Sahaabah (may Allah be pleased with them) on the necessity of appointing a caliph, after the death of the Prophet (blessings and peace of Allah be upon him). Therefore the Muhaajireen and Ansaar met in the saqeefah of Banu Saa‘idah for that purpose, before the Prophet (blessings and peace of Allah be upon him) was buried, then they agreed to appoint Abu Bakr as-Siddeeq (may Allah be pleased with him) as caliph.
Among the first examples of consensus after that was the agreement of the Sahaabah on fighting the apostates, after some initial objection on the part of ‘Umar (may Allah be pleased with him), but then Allah opened his heart and caused him to feel at ease with the decision of Abu Bakr, and the Sahaabah agreed on that, without any dissent.
Imam Abu’l-Hasan al-Ash‘ari (may Allah have mercy on him) said: Allah, may He be glorified and exalted, praised the Muhaajireen and Ansaar, and the earliest Muslims; the Qur’an speaks highly of the Muhaajireen and Ansaar in many places, and praises those who were present at Bay‘at ar-Ridwaan [when the Muslims affirmed their allegiance to the Prophet (blessings and peace of Allah be upon him) at al-Hudaybiyyah]. Allah, may He be glorified and exalted, says (interpretation of the meaning):
“Certainly was Allah pleased with the believers when they pledged allegiance to you, [O Muhammad], under the tree”
[al-Fat-h 48:18].
These people whom Allah praised agreed to appoint Abu Bakr as-Siddeeq (may Allah be pleased with him) as their leader; they called him Khaleefat Rasool-Allah (the Successor to the Messenger of Allah (blessings and peace of Allah be upon him)), and swore allegiance to him, rallying behind him and affirming his virtue, for he was the best of the Sahaabah in the qualities that are required for a person to be a leader, such as knowledge, asceticism, wisdom, leadership abilities, and so on.
End quote from al-Ibaanah fi Usool ad-Diyaanah, p. 66
And he (may Allah have mercy on him) said: What confirms the fact that Abu Bakr’s appointment as caliph was based on a strong foundation is the fact that all the Muslims rallied behind him and accepted his leadership.… Later on, we see that ‘Ali and al-‘Abbaas swore allegiance to him and agreed to accept his leadership. Therefore his leadership, after the death of the Prophet (blessings and peace of Allah be upon him), was based on the consensus of the Muslims.
It is not appropriate for anyone to say that what was in the hearts of ‘Ali and al-‘Abbaas [concerning the appointment of Abu Bakr as caliph] was something other than what they showed. If that argument was valid, then it would be almost impossible to establish consensus. The same argument could be used with regard to any consensus of the Muslims, but that would lead to the invalidation of the idea of consensus as binding proof, because Allah, may He be glorified and exalted, has not obliged us to know what is hidden in people’s minds when it comes to the matter of consensus; rather He has obliged us to go by what people appear to be. Therefore consensus and agreement on the appointment of Abu Bakr as-Siddeeq as caliph did indeed occur.
End quote from al-Ibaanah, p. 66
Imam Abu ‘Uthmaan as-Saabooni (may Allah have mercy on him) said: The scholars of hadith confirmed the validity of Abu Bakr’s appointment as caliph after the death of the Messenger of Allah (blessings and peace of Allah be upon him), because he was chosen by the Sahaabah; they were unanimously agreed on that and they all said: The Messenger of Allah (blessings and peace of Allah be upon him) was pleased that he should lead us in our religious matters (prayers), therefore we are pleased for him to lead us in our worldly matters. In other words, the Prophet (blessings and peace of Allah be upon him) appointed him to lead the people in the obligatory prayers when he was sick, which is their religious affairs, so we accept him as the successor of the Messenger (blessings and peace of Allah be upon him) with regard to our worldly affairs.
When they said, The Messenger of Allah (blessings and peace of Allah be upon him) put you ahead of us, so how could we put you back? What they meant was: the Messenger of Allah (blessings and peace of Allah be upon him) put you ahead to lead us in prayer when he was sick, and we prayed behind you on his orders, so how could we put you back after he put you forward?
The Messenger of Allah (blessings and peace of Allah be upon him) spoke highly of Abu Bakr when he was alive, which indicated to the Sahaabah that he was the most deserving of being appointed caliph after him. Hence they agreed to rally behind him, and that was to their own benefit, and they gained honour and victory through him.
End quote from ‘Aqeedat as-Salaf wa As-haab al-Hadith, p. 290.
We shall mention here the story of how ‘Ali (may Allah be pleased with him) swore allegiance to Abu Bakr as-Siddeeq on the first day.
Ibn Katheer (may Allah have mercy on him) said: al-Haafiz Abu Bakr al-Bayhaqi said: Abu’l-Hasan ‘Ali ibn Muhammad ibn ‘Ali al-Haafiz al-Isfaraayeeni informed us: Abu ‘Ali al-Husayn ibn ‘Ali al-Haafiz told us: Abu Bakr Muhammad ibn Is-haaq ibn Khuzaymah and Ibraaheem ibn Abi Taalib told us: Bandaar ibn Bashaar told us: Abu Hishaam al-Makhzoomi told us: Wuhayb told us: Dawood ibn Abi Hind told us: Abu Nadrah told us, from Abu Sa‘eed al-Khudri, who said:
The Messenger of Allah (blessings and peace of Allah be upon him) passed away and the people, including Abu Bakr and ‘Umar, gathered in the house of Sa‘d ibn ‘Ubaadah.
The spokesman of the Ansaar stood up and said: Do you know that the Messenger of Allah (blessings and peace of Allah be upon him) was one of the Muhaajireen, and his successor is one of the Muhaajireen, and we are the Ansaar (helpers) of the Messenger of Allah (blessings and peace of Allah be upon him), and we will be the Ansaar (helpers) of his successor as we were his helpers?
‘Umar ibn al-Khattaab stood up and said Your spokesman has spoken the truth. If you had said something other than this, we would not have accepted that. And he took the hand of Abu Bakr and said: This is the right man, so swear allegiance to him. ‘Umar swore allegiance to him, and the Muhaajireen and Ansaar swore allegiance to him.
Then Abu Bakr ascended the minbar and looked at the people, and he did not see az-Zubayr.
So he called for az-Zubayr, and he came.
Abu Bakr said: (You are) the son of the paternal aunt of the Messenger of Allah (blessings and peace of Allah be upon him) and his disciple; do you want to cause division among the Muslims?
He said: There is nothing to worry about, O successor of the Messenger of Allah. Then he stood up and swore allegiance to him.
Then Abu Bakr looked at the people, and he did not see ‘Ali, so he called ‘Ali ibn Abi Taalib and he came.
Abu Bakr said: (You are) the son of the paternal uncle of the Messenger of Allah (blessings and peace of Allah be upon him) and his son-in-law; do you want to cause division among the Muslims?
He said: There is nothing to worry about, O successor of the Messenger of Allah. Then he stood up and swore allegiance to him.
Abu ‘Ali al-Haafiz said: I heard Muhammad ibn Is-haaq ibn Khuzaymah say: Muslim ibn al-Hajjaaj came to me and asked me about this hadith, so I wrote it down for him on a piece of paper and I read it to him. This hadith is worth a badanah (a valuable camel); indeed it is worth a badrah (sack of money)!
End quote from al-Bidaayah wa’n-Nihaayah by Ibn Katheer (5/269).
A badrah is a big sack full of money; it was said that it is one thousand or ten thousand dirhams, or seven thousand dinars.
Al-Mu‘jam al-Waseet (p. 43); al-Qaamoos al-Muheet (p. 444).
Then Ibn Katheer narrated a report about another oath of allegiance that ‘Ali swore after the death of Faatimah (ma y Allah be pleased with her). He said: This oath of allegiance that was sworn by ‘Ali (may Allah be pleased with him) to Abu Bakr (may Allah be pleased with him) after the death of Faatimah (may Allah be pleased with her) was in confirmation of the reconciliation between them and it was secondary to the oath of allegiance mentioned above, that was sworn on the day of as-saqeefah, as was narrated by Ibn Khuzaymah and classed as saheeh by Muslim ibn al-Hajjaaj. ‘Ali did not keep his distance from Abu Bakr, during these six months; rather he used to pray behind him, and he was present when Abu Bakr used to meet with some of the senior Sahaabah in order to seek their advice concerning some issues; he was also willing to ride with him on a campaign to Dhu’l-Qassah.
In Saheeh al-Bukhaari it says that Abu Bakr (may Allah be pleased with him) prayed ‘Asr a few days after the Messenger of Allah (blessings and peace of Allah be upon him) died, then he went out of the mosque and found al-Hasan ibn ‘Ali playing with some boys. He carried him on his shoulder and started saying: May my father be sacrificed for the one who looks like the Prophet and does not look like ‘Ali! And ‘Ali smiled (at this joke).
But when this second oath of allegiance occurred, some narrators thought that ‘Ali had not sworn allegiance (to Abu Bakr) before that, so they denied that (the first oath of allegiance) had happened. But if someone confirms that something happens, that takes precedence over the report of someone who says that it did not happen, as we have mentioned and explained above. And Allah knows best.
End quote from al-Bidaayah wa’n-Nihaayah (5/307)
And Allah knows best.