Part of the maxims and principles for Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah is that it is prohibited to excommunicate from Islam a Muslim for no reason
Ibn ‘Umar (may Allah be pleased with them both him and his father) says that the Messenger of Allah ? stated, “Any person who says to his brother, ‘O Kaafir (disbeliever).’ Then one of them has returned with that label; if he (the person told) is as he (the teller) stated, then that is fine; otherwise, the label returns to him (the teller).” [87] Al-Bukhaaree (6104) abbreviated, and Muslim (60) and the wording is his.
Ibn ‘Abd al-Barr comments, “The meaning in this statement according to the scholars of Fiqh and Hadeeth from Ahl as-Sunnah wa al-Jamaa’ah is that it is prohibited for a Muslim to declare or claim that his Muslim brother is excommunicated from Islam due to a sin or an interpretation that does not remove him from Islam according to everyone. The prohibition about excommunicating from Islam a Muslim in this hadeeth and others has been conveyed informatively rather prohibitively. This style is found both in the Quran and the Sunnah and is well known in the language of the Arabs …. This an extreme form of warning within this prophetic statement as well as it contains prohibition from telling anyone from the people of the Qiblah Muslims: ‘O Kaafir.’” [88] At-Tamheed (17/14-22)
Among the maxims and principles for Takfeer amongst Ahl as-Sunnah wa al-Jamaa’ah: Avoiding Takfeer for every sin
Part of the creed of Ahl as-Sunnah wa al-Jamaa’ah is that they do not excommunicate from Islam anyone from the people of the Qiblah Muslim for every sin as long as he does not deem it permissible, and the sin they imply is of that kind whose committer does not become a disbeliever thereby.
Ibn Taymiyyah mentions about the creed of the pious predecessors, “Despite this, they do not excommunicate from Islam anyone from the people of the Qiblah just for the acts of disobedience and major sins, as the Khawaarij do; in fact, the faith-based brotherhood remains regardless of the acts of disobedience. This is as Allah, the Sublime and the Exalted, mentioned in the ayah concerning the legal retribution, “One who is pardoned by his brother, then the recourse (of the latter) is to pursue (the former) with fairness.” Al-Baqarah: 178 Allah, the Exalted, also states, “And if two factions among the believers should fight, then make settlement between the two. But if one of them oppresses the other, then fight against the one that oppresses until it returns to the ordinance of Allah. And if it returns, then make settlement between them in justice and act justly. Indeed, Allah loves those who act justly.” Al-Hujurat: 9, He, the Almighty, also states, “The believers are but brothers, so make settlement between your brothers.” Al-Hujurat: 10 [89] See: Al-‘Aqeedah al-Waasitiyyah, p.113.
Ibn Uthaymeen says, “According to Ahl as-Sunnah wa al-Jamaa’ah, a Muslim does not become a disbeliever just by committing acts of disobedience and major sins. A believer who commits a major sin still has the faith. The core belief is still present in him; however, its perfection is not there.” [90] See: Sharh Al-‘Aqeedah al-Waasitiyyah, (2/237-239).
Part of maxims and principles concerning Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah is that ‘he whose Islam is established with certainty, it is not allowed to excommunicate him from Islam without certainty.’
Ibn Taymiyyah states, “He whose Islam is established with certainty, that cannot disappear by mere doubt, in fact it still remains until after the establishment of a clear proof or removal of any obscurity about the apostacy.” [91] See: Majmoo’ Al-Fataawaa, (12/466).
Muhammad ibn ‘Abd al-Wahhaab says, “If anyone displays Islam and we think that he has committed a nullifying act, then we do not excommunicate him from Islam based on the assumption. That is because assumption cannot uplift certainty.” [92] See: Ad-Durar As-Saniyyah fi Al-Ajwibah An-Najdiyyah, (10/112).
Part of the maxims and principles concerning Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah is ‘to rule according to what is apparent.’
Ibn Taymiyyah says, “The faith on which the worldly rulings are suspended is that belief, which is apparent, that is, Islam.” [93] Al-Imaan, p.325.
Ibn Hajar states, “All the scholars hold the consensus that the rulings of the world are applied what is apparent and Allah takes care of the internal secrets.” [94] Fath al-Baaree, 12/273.
The proofs concerning this maxim are plentiful, of which are the following:
Allah, the Exalted, states, “O you who have believed, when you go forth to fight in the cause of Allah, investigate; and do not say to one who gives you a greeting of peace, ‘You are not a believer,’ aspiring for the goods of worldly life.” (An-Nisaa’: 94)
It is narrated on the authority of Usaamah ibn Zayd (may Allah be pleased with him) who says, “The Messenger of Allah ? sent us in a raiding party. We raided Hurooqaat of Juhaynah [95] The Arabic word al-Huruqaat [from Juhaynah]: a people from the Juhaynah tribe. in the morning. I caught hold of a man and he said: ‘There is no god but Allah,’ I attacked him with a spear. It affected in myself, and I talked about it to the Apostle ?. The Messenger of Allah ? said: ‘So he professed that there is no god but Allah, yet you killed him?’ I said: ‘O Messenger of Allah, he professed it out of fear of the weapon.’ He (the Holy Prophet) observed: ‘Why did you not tear his heart then to find out whether he had professed or not?’ And he went on repeating it to me till I wished I had embraced Islam that day.” [96] Al-Bukhaaree (6872), Muslim (96), and the wording is his.

An-Nawawee comments, “Its meaning entails that you are legally responsible only for the outward display of faith and what the tongue utters. As for the heart, you have no way to know what is in it.” [97] Explanation (Sharh) of al-Nawawee on Muslim, (2/104).

Among the maxims and principles concerning Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah is the ascertainment about the news of a Muslim falling into disbelief.
Allah, the Exalted, states, “O you who have believed, if there comes to you a disobedient one with information, investigate, lest you harm a people out of ignorance and become, over what you have done, regretful.” Al-Hujurat: 6
Ash-Shawkaanee explains, “The meaning of investigation entails to fully identify and scrutinise properly. Part of ascertaining is deliberateness without rushing. It also means to carefully consider the occurred matter and reaching news until it becomes clear and apparent.” [98] Fath Al-Qadeer, (5/71).
Allah, the Sublime, states, “O you who have believed, when you go forth to fight in the cause of Allah, investigate; and do not say to one who gives you a greeting of peace, ‘You are not a believer,’ aspiring for the goods of the worldly life.” An-Nisaa’: 94
Ibn Jareer says, “In war, take your time and fully consider killing one whose belief-related affair is obscure to you. You have not known the reality of his Islam and disbelief. Do not rush lest you kill a person whose belief-related matter is ambiguous to you. Do not advance towards killing anyone except towards killing the one concerning whom you certainly know that he is at war with you, Allah and His Messenger.” [99] Tafseer of Ibn Jareer, (7/351).
Muhammad ibn ‘Abd al-Wahhaab says, “We do not excommunicate from Islam a person about whom we have not known to hold disbelief, just because of a nullifier that has been mentioned about him, while we have not fully investigated it.” [100] Ad-Durar as-Saniyyah fi al-Ajwibah an-Najdiyyah, 10/112.
Part of the maxims and principles concerning Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah is ‘to ascertain whether what emanates from a Muslim is actually clear disbelief according to the scholars; and to avoid Takfeer based on outcomes and that which is necessitated unless that which is necessitated is adopted.’
Allah, the Exalted, states, “And do not pursue that of which you have no knowledge.”  Al-Israa’: 36 
Ibn Katheer says, “Allah, the Exalted, prohibited from making statements without knowledge, even with assumption/suspicion which entails supposition and mere imagination as Allah, the Exalted, states, “O you who have believed, avoid much negative assumption. Indeed, some assumption is sin.” Al-Hujurat: 12 It comes in a hadeeth: “Beware of suspicion, as suspicion is the falsest tale.’” [101] Al-Bukhaaree (5143) and Muslim (2563) at length from the hadeeth of Aboo Hurayrah (may Allah be pleased with him). [102] Tafseer Ibn Katheer, (5/75).
Ibn ‘Abd al-Barr states, “The obligatory point in terms of juristic judgement is that none will be excommunicated from Islam apart from the one upon whose being disbelief everyone has agreed, or a proof has been established against him for him to be excommunicated from Islam, while there is no evidence in his favour from the Quran or the Sunnah.” [103] At-Tamheed, (17/22).
Thus, it is not permissible to excommunicate from Islam anyone due to the statements or acts which contain different possibilities in terms of their reference before the objective of their utterer or doer is fully established; it is also not permissible to excommunicate from Islam someone because of the outcome of his statement or what it necessitates.
Ibn Hazm says, “As for the one who excommunicates from Islam people based on how their statements may be construed (in his mind), then that is a mistake because that is a lie against the adversary and is putting words into his mouth that he did not say.” [104] Al-Fasl Fee al-Milal wa al-Ahwaa’ wa an-Nihal, (3/139).
Ibn Hajar states, “What is apparent concerning the one who deserves to be declared out of the fold of Islam is he whose disbelief is clearly stated, and the one whose statement necessitates disbelief, and after this issue is presented to him, he confirms that he adheres to that which his statement nesseciates. However, the one who does not adhere to it, even if he defends it, he does not become a disbeliever, even though the deductible meaning extrapolated therefrom was an item of disbelief.” [105] Fath al-Mugheeth, as-Sakhaawee, 2/73.
Part of the maxims and principles concerning Takfeer according to Ahl as-Sunnah wa al-Jamaa’ah that ‘for no particular person can there be a decision of his entry into Paradise or Hell.’
Ibn Taymiyyah says, “A particular person cannot be bore witness of entry to Paradise unless there is a specific proof for that, neither can any particular person be testified to enter Hell unless there is a specific proof for that. They cannot be witnessed based on mere assumption due to their insertion in the generality.” [106] Majmoo’ al-Fataawaa (35/68).
He also stated, “We maintain a statement of generality concerning the texts regarding promises, warnings, Takfeer, and rendering someone a disobeyer; however, we do not decide on placing a particular person within that generality until a requirement without an opposer is established.” [107] Majmoo’ al-Fataawa, (28/501).
Ibn Uthaymeen says, “As for bearing witness concerning apostasy, we bear witness that this certain unbelieving person who openly practices disbelief and takes pride in it, we bear witness that he is a disbeliever, and we bear witness that he died on disbelief as long as it is not apparent to us that he repented. However, we cannot bear witness about his entry to Hellfire as this is an unseen act …. Part of the methodology of Ahl as-Sunnah wa al-Jamaa’ah is that they do not bear witness about entry to Paradise or Hellfire for any particular person apart for the one whom the Prophet ? bore witness.” [108] Liqaa’ al-Baab al-Maftooh, (meeting number: 165).                                                
Part of the maxims and principles of Takfeer is the availability of conditions and lack of impediments.
Ibn Taymiyyah states, “The establishment of the ruling concerning Takfeer regarding a particular person contingent to the realisation of conditions and non-existence of impediments.” [109] Al-Mustadrak ‘ala Majmoo’ Al-Fataawa. 1/139.
He also stated, “A particular person amongst the people of the Qiblah cannot be testified to enter Hellfire because of the permissibility of that fact that a warning has not reached him due to either a condition being absent or a hindrance establishing. It is possible that the prohibition might have not reached him, and he might have repented from committing that prohibited thing and perhaps he has great good deeds that erase the punishment of that prohibited thing, or perhaps, he might be tested with calamities that expiate that sin from him or an intercessor who is obeyed may intercede on his behalf. Similarly, is the case concerning the statements whose maker becomes a disbeliever; perhaps the textual proofs which require the knowledge of truth might have reached the person, or they might be with him, however, they might have not confirmed with him, or he has not been able to understand it. Or some doubts might have appeared before him, however, Allah excused him for them. Hence, if anyone from the believers expends his effort in making a judgement in pursuit of truth and then he makes a judgemental error, then Allah forgives his error, whatever it may be, irrespective whether that pertains to theoretical issues or actional matters. This is the view of the companions of the Prophet ? and most of the leading scholars of Islam.” [110]  Majmoo’ al-Fataawa. 23/345.