The Conditions for the Establishment of Proof in Declaring a Person to be an Innovator
By ash-Shaikh al-‘Allāmah Rabī’ bin Hādī al-Madkhalī
Question posed to Shaikh Rabī’ bin Hādī (may Allāh preserve him) :
“Our Shaikh, may Allāh preserve you, there is a question here circulating amongst the students of knowledge, and that is: Is the establishment of proof a condition when performing tabdī’  upon the one who fell into an innovation or innovations or is it not a condition? Benefit us, may Allāh reward you with good.”
It is well known from ahlus-Sunnah that whoever fell into an affair necessitating unbelief that takfīr  is not performed until the proof is established upon him.
As for the one who falls into an innovation, then he is of categories.
The first category: Ahlul-Bid’ah such as the Rawāfid, the Khawārij, the Jahmiyyah, the Qadariyyah, the Mu’tazilah, the Grave-worshipping Sūfīs, the Murji’ah, and whoever is connected to them [in our times] such as al-Ikhwān, at-Tablīgh and those similar to them. For these innovations the Salaf did not make it a condition that the proof be established due to the fact that the ruling upon them is [in accordance to] the innovation. So regarding the Rāfidī, it is said about him, “Innovator (mubtadi’)”. As for the Khārijī, it is said about him, “Innovator”, and so on, regardless of whether the proof is established upon him or not.
The second category: The one who is from ahlus-Sunnah and then he fell into a clear-cut innovation such as the saying that the Qur’ān is created, or the denial of the Pre-Decree, or he has the views of the Khawārij or other than that. Then upon this person tabdī’ is performed, i.e. he is declared an innovator – and this was the behavior of the Salaf. An example of this is what is narrated from Ibn ‘Umar (radi Allaahu ‘anhu), when he was asked regarding the Qadariyyah, he answered: “When you meet them, inform them that I am free from them, and they are free from me.” 
The third category: Someone who was from ahlus-Sunnah, well known for seeking the truth but he fell into a subtle bid‘ah. So if this person dies, then it is not permitted to make tabdī’ of him, rather he is mentioned with good. And if he is alive, he is advised and the truth is made clear to him, and one does not hasten to make tabdī’ of him, but if he persists [upon innovation], then he is declared an innovator.
Shaikhul-Islām Ibn Taymiyyah (rahimahullaah, died 728H) stated:
“There are many from the Mujtahidīn (Scholars) of the Salaf and of later times who spoke with and acted upon innovation whilst not knowing it to be an innovation. This was either due to weak ahadīth that they thought were authentic; or Quranic Verses they understood in an incorrect manner; or due to an opinion one would hold in an issue because the texts had not reached him. So if a man fears his Lord to the best of his ability, he enters into the saying of Allāh: “Our Lord, do not take us to account if we are forgetful or mistaken.” And there occurs in a hadīth that Allāh stated [in response]: “I have done so.” And this matter has been explained in another place.” 
Nevertheless the point is that it is not permitted to place unrestricted conditions regarding the establishment of proofs upon ahlul-Bid’ah in general, and nor negate these conditions unrestrictedly – and the affair is as I have mentioned.
So my advice to the students of knowledge is that they hold fast to the Book and Sunnah and that they are disciplined and grounded upon the Manhaj of the Salaf in every aspect of their Religion – and specifically in the arena of takfīr, tafsīq  and tabdī’ so that there is not excessive disputing and argumentation in these matters.
I particularly advise and encourage the Salafī youth that they abandon those affairs that sow malice, rancor, differing and splitting – affairs that are hated by Allāh and which He warned against – affairs that the noble Messenger (salallaahu ‘alaihi wassallam), the Companions and the Righteous Salaf warned against. Also [I advise] the Salafī youth to strive to spread those affairs that lead to love, affection and brotherhood between them – those affairs that are loved by Allāh (the Mighty and Majestic) and His Messenger (salallaahu ‘alaihi wassallam).
May the salutations and peace of Allāh be upon our Prophet, his family and his Companions.
__________ Answered by the Shaikh, in writing on 24th Ramadān 1424AH. Posted on www.sahab.net/ in Arabic. Before you is an abridged translation of the original for the sake of brevity.  Tabdī’ is to declare a Muslim to be an Innovator and therefore outside the sphere of ahlus-Sunnah wal-Jamā’ah.  Takfīr is to declare a person to be an unbeliever outside the fold of Islām.  Reported by Muslim.  Ma’ārij al-Wusūl, p. 43.  Tafsīq is to declare a Muslim to be an open rebellious sinner.