What Is Takfir?
Question

We hope that you can define the guidelines by means of which it is possible to determine whether someone is a kafir or fasiq, so that I will not fall into the innovations into which many groups have fallen. Which books do you advise me to read? Please note that I am a beginner seeker of knowledge.
Praise be to Allah.Does Islam allow us to judge others?
Determining whether someone is a kafir or a fasiq is not up to us, rather it is up to Allah, may He be exalted, and His Messenger (peace and blessings of Allah be upon him). This is one of the rulings of Shari`ah that is to be referred to the Quran and Sunnah, so we should be very careful and base our judgement on clear proof. 
No one may be judged to be a kafir or fasiq except the one whom the Quran and Sunnah indicate is a kafir or fasiq. 
People are judged according to what is apparent from them
The basic principle is that the one who appears outwardly to be a Muslim of good character is regarded as still being a Muslim of good character, until it is proven that this is no longer the case by means of evidence that is acceptable in Shari`ah. 
Can we take judging others’ faith lightly?
It is not permissible to take lightly the matter of judging someone to be a kafir or fasiq, because that involves two very serious matters: 

It implies fabricating lies against Allah with regard to this ruling, and fabricating lies against the one who is being judged. 
Falling into that which one accused one’s brother of, if he is free from that. 

In Sahih al-Bukhari (6104) and Sahih Muslim (60) it is narrated from ‘Abd-Allah ibn ‘Umar (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “If a man declares his brother to be a kafir, it will apply to one of them.”  According to another report, “Either it is as he said, otherwise it will come back to him.” 
What should we consider before judging others’ faith?
Based on this, before ruling that a Muslim is a kafir or a fasiq, two things must be examined: 

The evidence of the Quran or Sunnah that this word or this action implies that a person is a kafir or a fasiq. 
Applying this ruling to a specific person who says or does that thing, such that the conditions of judging a person to be a kafir or fasiq will be met in his case, and there are no impediments.  

Among the most important of these conditions are the following: 

That he should be aware of his transgression that renders him a kafir or fasiq, because Allah says (interpretation of the meaning): 

“And whoever contradicts and opposes the Messenger (Muhammad صلى الله عليه وسلم) after the right path has been shown clearly to him, and follows other than the believers’ way, We shall keep him in the path he has chosen, and burn him in Hell — what an evil destination!.” [Al-Nisa 4:115] 
“And Allah will never lead a people astray after He has guided them until He makes clear to them as to what they should avoid. Verily, Allah is the All-Knower of everything.” [Al-Tawbah 9:115]
Hence the scholars said that a person who denies obligatory duties should not be judged to be a kafir if he is new in Islam, until that has been explained to him. 

A reason why he cannot be ruled to be a kafir or fasiq is if he does something that incurs such a judgement involuntarily. This may take several forms such as: 


For example, he may be forced to do that, so he does that because he is forced to, not because he accepts that. He is not a kafir in that case, because Allah says (interpretation of the meaning): 

“Whoever disbelieved in Allah after his belief, except him who is forced thereto and whose heart is at rest with Faith; but such as open their breasts to disbelief, on them is wrath from Allah, and theirs will be a great torment.” [Al-Nahl 16:106]

Another example is when he is not thinking straight, so he does not know what he is saying because of extreme joy or sorrow or fear and so on. The evidence for that is the report narrated in Sahih Muslim (2744) from Anas ibn Malik (may Allah be pleased with him) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Allah rejoices more over the repentance of His slave when he repents to Him than one of you who was on his mount in the wilderness, then he lost it, and his food and drink are on it, and he despairs of finding it. He goes to a tree and lies down in its shade, having lost hope of finding his mount, and whilst he is like that, there it is standing in front of him, so he takes hold of its reins and says, because of his intense joy, ‘O Allah, You are my slave and I am your lord,’ making this mistake because of his intense joy.” 


Misinterpretation . He may have some confusion and some misinterpretation that he adheres to, thinking that it forms evidence for his beliefs, or he may not be able to understand and comprehend shar’i evidence and proof in the proper way. Therefore, judging someone to be a kafir is not valid except in the case of one who deliberately goes against the shar’i evidence and who knows that he is wrong. 

Allah says (interpretation of the meaning): 
“And there is no sin on you concerning that in which you made a mistake, except in regard to what your hearts deliberately intend. And Allah is Ever Oft-Forgiving, Most Merciful.” [Al-Ahzab 33:5]
Ibn Taymiyah (may Allah have mercy on him) said in Majmu’ al-Fatawa (23/349): 
“Imam Ahmad (may Allah be pleased with him) prayed for mercy for them (i.e., the caliphs who were influenced by the view of the Jahmis who claimed that the Quran was created, and supported it) and prayed for forgiveness for them, because he knew that it was not clear to them that they were disbelieving the Messenger and denying what he had brought, rather they misinterpreted and erred, and followed those who said that to them.”
And he (may Allah have mercy on him) said in Majmu’ al-Fatawa (12/180): 
“With regard to takfir (judging someone to be a kafir), the correct view is that a member of the ummah of Muhammad (peace and blessings of Allah be upon him) who strives to reach the truth concerning a certain issue, but reaches the wrong conclusion, is not to be deemed a kafir, rather he will be forgiven for his mistake. But the one who understands the message brought by the Messenger, but deliberately goes against the way of the Messenger (peace and blessings of Allah be upon him) after true guidance has become clear to him, and follows a path other than that of the believers, is a kafir . The one who follows his whims and desires and fails to seek the truth and speaks without knowledge is a disobedient sinner, and may be a fasiq, but he may have some good deeds that outweigh his bad deeds.”
And he (may Allah have mercy on him) said: (3/229): 
“However, and those who sit with me know this about me, I am always one of those who most emphatically forbid describing a specific person as a kafir, fasiq or sinner, unless it is known that shar’i proof has been established against him, and it has been proven whether he is a kafir, a fasiq or a sinner. I affirm that Allah has forgiven this ummah for its mistakes, which includes mistakes in narrative and practical issues. The salaf continued to debate many of these issues but none of them testified that anyone else was a kafir or a fasiq or a sinner.” 
He mentioned some examples, then he said: 
“I also state that what has been narrated from the salaf and the imams, stating that the one who says such and such is a kafir, is also true, but it is essential to differentiate between general rules and specific cases. 
… Takfir is a kind of warning ; even though the words may be a rejection of what the Messenger (peace and blessings of Allah be upon him) said, the man may be new in Islam, or he may have grown up in a remote region. Such a person cannot be ruled to be a kafir, no matter what he denies, unless proof has been established against him. The man may not have heard of those texts, or he may have heard them but they were not proven to him , or he may have some ideas that are contrary to what he heard, that led him to misinterpret the text.  
I always remember the hadith in al-Sahihayn, which speaks of the man who said: “ ‘When I die, burn me and crush (my bones), then scatter me in the sea, for by Allah, if Allah grasps hold of me He will punish me as He has not punished anyone else in the world.’ They did that, and Allah said: ‘What made you do what you did?’ He said: ‘Fear of You.’ And He forgave him.” 
This man doubted the power of Allah and doubted that He would restore him if his remains were scattered; rather he believed that he would not be resurrected, which is kufr according to the consensus of the Muslims. But he was ignorant and did not know about that; however, he was a believer who feared that Allah would punish him, so He forgave him because of that. 
One who is qualified to engage in ijtihad and who bases his incorrect notion on some misinterpretation of some text but is sincere in his keenness to follow the Messenger (peace and blessings of Allah be upon him) is even more deserving of forgiveness than such a person.” (Based on Khatimah al-Qawa’id al-Muthla by Shaykh Ibn ‘Uthaymin (may Allah have mercy on him).) 
Because the matter of takfir is so serious, and mistakes therein are so grave, the seeker of knowledge, especially if he is a beginner, should refrain from indulging in that, and he should focus on acquiring beneficial knowledge that will set his own affairs straight in this world and the Hereafter. 
Importance of seeking knowledge before indulging in judging peoples’ faith
Before we suggest some books to you, we should advise you to seek knowledge directly from scholars of Ahl al-Sunnah, because that is the easiest and safest way; but that is subject to the condition that the one from whom you learn is trustworthy in terms of his knowledge and religious commitment and following of the Sunnah, and in avoidance of whims and desires and innovations. 
Muhammad ibn Sirin (may Allah have mercy on him) said: “This knowledge is the (foundation of) religion, so watch from whom you learn your religion.”  (Narrated by Muslim in the Introduction to his Sahih) 
If it is not possible where you are to attend lessons given by scholars, then you can make use of their tapes, as it has become easy to obtain them on CDs and websites, praise be to Allah. You can also benefit from some seekers of knowledge who are keen to acquire shar`i knowledge and follow the Sunnah; hardly any place is without such people, in sha Allah. 
Best introductory books on Islam
Books which you should strive to acquire and study include the following: 

Tafsir: Tafsir Ibn Sa’di; Tafsir Ibn Kathir. 
Hadith: al-Arba’in al-Nawawiyyah (al-Nawawi’s 40), with a commentary thereon; al-Ihtimam bi Jami’ al-‘Ulum wa’l-Hikam by Ibn Rajab; Riyad al-Salihin – you may pay special attention to this blessed book, and you can also learn from the commentary thereon by Shaykh Ibn ‘Uthaymin (may Allah have mercy on him). 
`Aqidah: Study Kitab al-Tawhid by Shaykh Muhammad ibn ‘Abd al-Wahhab, with its commentary; al-‘Aqidah al-Wasitiyyah by Shaykh al-Islam Ibn Taymiyah; some other useful essays on this topic such as Tahqiq Kalimat al-Ikhlas by Ibn Rajab and al-Tuhfah al-‘Iraqiyyah fi’l-A’mal al-Qalbiyyah by Ibn Taymiyah. 
You can also benefit from Zad al-Ma’ad by Ibn al-Qayyim (may Allah have mercy on him) and many of his other books such as al-Wabil al-Sayyib and al-Da wa’l-Dawa. 

This is a start. If you study these books, especially if there is someone who can help you to read and understand them, then you can move on to other books, in sha Allah.
And Allah knows best.