Imaam Bukhaaree (rahimahullaah) said:
I met more than a thousand men amongst the people of
knowledge from the people of al-Hijaaz, al-Makkah, al-Madinah, al-Koofah, al-Basrah, Waasit, Baghdaad, Shaam and Misr... and I never saw a single one of them differ with respect to the following matters...
... And they used to forbid and prevent [people] from the innovations - those that the Messenger and his Companions were not upon, due to His saying:
And hold fast, all of you together, to the Rope
of Allâh (i.e. this Qur'ân), and be not divided among yourselves
[Soorah Aali Imraam 3:103]
and due to His saying:
If you obey him [the Messenger], you shall be on
the right guidance [Soorah an-Noor 24:54]
[Reported by al-Laalikaa'ee (2/172-5), The Creed of Imaam Bukhaaree p.13,28 - al-Maktabah as-Salafiyyah Publications]
In the words of Imaam Bukhaaree is a clear indication that Muslim unity is to be attained by removing the innovations - and that is the unanimous understanding of the greatest of scholars of the noble ayah in question. Since it is the newly-invented matters (in the issues of belief, action and methodology) that have divided the hearts of the Muslims and set them against each other. Thus, in order for the hearts of the Muslims to unite and consequently, their word and rank, it is necessary for them to purify their beliefs, actions and methodologies from everything that was never taught by the Messenger and which was never acted upon by the Noble Companions (ra) - whilst humbly submitting to the Pure and Clear Sunnah. But this cannot be attained until the Muslims attend to the authentic and beneficial knowledge - that which has been left by the Messenger and which has been inherited by the Scholars after him, the Ahl ul-Hadeeth (the People of Authenticating the Narrations) and then to nurture themselves upon it. This issue was so clearly understood by the Companions of Allaah's Messenger and those after them, as will become evident by the narrations below.
The Messenger of Allaah said: Every innovation is misguidance and going astray. Reported by Abu Daawood, no.4607 and it is saheeh.
The Messenger also warned against the people of innovation, from befriending, supporting or taking from them saying: Whoever innovates or accomodates an innovator then upon him is the curse of Allaah, His Angels and the whole of mankind. Reported by Bukhaaree (12/41) and Muslim (9/140)
And in his footsteps, we find the Noble Companions and the Taabieen after them warning from the danger of innovations upon the Ummah, its people and their unity.
Ibn Abbaas (d. 68H) said: Indeed the most detestable of things to Allaah are the innovations. Reported by al-Bayhaqee in as-Sunan al-Kubraa (4/316)
Ibn Umar (d. 84H) said: Every innovation is misguidance, even if the people see it as something good. Reported by Abu Shaamah (no. 39)
Sufyaan ath-Thawree (d. 161H) said:Innovation is more beloved to Iblees than sin, since a sin may be repented from but innovation is not repented from. Reported by al-Laalikaa'ee (no. 238)
Al-Fudayl bin 'Iyaad (d. 187H) said: I met the best of people, all of them people of the Sunnah and they used to forbid from accompanying the people of innovation. Reported by al-Laalikaa'ee (no.267)
Al-Hasan al-Basree (d. 110H) said: Do not sit with the people of innovation and desires, nor argue with them, nor listen to them. Reported by ad-Daarimee in his Sunan (1/121)
Ibraaheem bin Maysarah (d.132H) said: Whoever honours an innovator has aided in the destruction of Islam. Reported by al-Laalikaa'ee (1/139).
Sufyaan ath-Thawree (d. 161H) said: Whoever listens to an innovator has left the protection of Allaah and is entrusted with the innovation. Reported by Abu Nu'aym in al-Hilyah (7/26) and Ibn Battah (no.444).
Imaam Maalik (d. 179H) said: How evil are the people of innovation, we do no give them salaam. Reported by al-Baghawee in Sharh us-Sunnah (1/234).
Imaam ash-Shaafi'ee (d. 204H) said: That a person meets Allaah with every sin except Shirk is better than meeting Him upon any one of the innovated beliefs. Reported by al-Bayhaqee in al-I'tiqaad (p.158)
Al-Fudayl bin 'Iyaad (d. 187H) said: Whoever sits with a person of innovation, then beware of him and whoever sits with a person of innovation has not been given wisdom. I love that there was fort of iron between me and a person of innovation. That I eat with a Jew and a Christian is more beloved to me than that I eat with a person of innovation. Reported by al-Laalikaa'ee (no.1149)
Al-Layth bin Sa'd (d. 175H) said: If I saw a person of desires (i.e. innovations) walking upon the water I would not accept from him." So Imaam as-Shaafi'ee then said: "He (al-Layth) has fallen short. If I saw him walking in the air I would not accept from him. Reported by as-Suyooti in al-Amr bil 'Ittibaa wan-Nahee anil Ibtidaa'.