Should he warn his friends against listening to this daa’iyah?
Question

I am warning my friends from listening to a specific dae’yah for the following reasons:
1- He said that Iblees did not disbelieve.
2- He said that the actors / artists will enter the Jannah because of their arts.
3- He said that the Jews are not our enemy. 
I am not saying what he did not say himself. I am saying this after I listened to his lectures while he says this. Please tell me if what I am doing haram. May Allah reward you.
Praise be to Allah.We appreciate your keenness for Islam but we must mention some important principles that every Muslim should follow. 
Firstly: 
Speaking about people is a serious matter, and praising them or criticizing them is something that is not to be taken lightly. Many scholars would refrain from talking about these matters because backbiting is a grievous sin, and the sin is compounded if the backbiting is about daa’iyahs, scholars or reformers. 
It was narrated from Abu Hurayrah that the Prophet (peace and blessings of Allaah be upon him) said: “Every Muslim is sacred to his fellow Muslim: his blood, his property and his honour.” Narrated by Muslim (2564). 
Ibn Daqeeq al-Eid said in al-Iqtiraah (34): 
Indulging in (maligning) the honour of the Muslims is one of the ditches of Hell. End quote.  
Being preoccupied with the mistakes of others and seeking them out is something with which people are afflicted nowadays. It would be better for them to seek beneficial knowledge and strive to speak good words and do good deeds. 
However, “backbiting” may be permissible or even obligatory, if it is aimed at warning the people against the evil of an evildoer, misguided person or follower of innovation. 
No one – including daa’iyahs and scholars – is infallible and free from error, rather no human can be free from error. 
But these errors are of two types: 
1 – Errors that clearly go against a clear text, or go against the consensus of the ummah. These errors must be pointed out, and it is not permissible to keep quiet about them. 
2 – Errors in matters that are subject to ijtihaad, such as those concerning which there is no definitive text to indicate the ruling, but there are texts which may be understood as pointing to the ruling, or there are differences of opinion as to their soundness, or there are no texts concerning them at all, rather they are matters that are regarded as subject to ijtihaad by the scholars, as is well known. It is not permissible to denounce them or the one who follows them, but there is nothing wrong with debating them and explaining the correct point of view, as each scholar see it.  
As for slandering the person himself and warning others against him, that varies according to the person and the extent of the error into which he has fallen, and the extent to which the Muslims benefit from his da’wah. If the man is calling people to a way other than the way of Ahl al-Sunnah wa’l-Jamaa’ah and is fighting the way of Ahl al-Sunnah, and praising other ways, or his way is based on innovated principles, even if he does not clearly declare that, then if there is some goodness in his message but the evil outweighs the goodness, he must be warned against lest the people be deceived by his words and he cause them to go astray. 
There are some people – daa’iyahs – who claim to belong to Ahl al-Sunnah wa’l-Jamaa’ah, and do not promote any other way, but they have so many wrong and weird ideas that the bad effects of their call outweigh the good, and they are wrong more than they are right. These too must be warned against. 
There is a third category of people who belong to Ahl al-Sunnah wa’l-Jamaa’ah, and who make some mistakes – which no human being can avoid – due to either misinterpretation or incorrect ijtihaad or weak knowledge or on the basis of what he believes is in the public interest of the Muslims and so on – but in general they adhere to the Sunnah, promote it and defend it, and their good aspects outweigh the bad, and the benefit that people get from their da’wah is greater than the harm that befalls some from following these mistakes. In this case we must point out the mistakes so as to warn people and advise them, and denounce evil, but it is not permissible to overstep the mark and slander the people themselves, or try to bring about their downfall and warn people against listening to them or learning from them, or accuse them of errors that they have not actually uttered. The fair-minded person can overlook a small slip if a person is mostly correct; what human being is ever right all the time and never makes a mistake?  
We will focus here on some important principles which we must observe when looking at and judging others.
1 – The first principle: the basis of his knowledge and actions. If a person is seeking to follow the Messenger (peace and blessings of Allaah be upon him) and venerate his sharee’ah, inwardly and outwardly, then he may be forgiven, in sha Allaah. 
Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said, discussing Abu Dharr al-Harawi, al-Baaqillaani, al-Baaji and other Ash’ari scholars: 
Moreover they all strove hard in the way of Islam and did good deeds, and refuted many of the proponents of heresy and innovation, and supported many of the Ahl al-Sunnah, as is obvious to anyone who knows anything about them, and who speaks of them with knowledge, sincerity, justice and fairness.  
But because they were confused about this principle that was originally taken from the Mu’tazilah [i.e., denying that deeds are done by choice], although they are good and wise, they needed to refute it, so (by way of refuting it) they may have said statements that Muslims of knowledge and religious commitment found unacceptable. Because of that, people took two approaches: some began to venerate them for their good qualities and virtues, and some criticized them because of the innovation and falsehood in some of what they said, but the best of ways is the middle way. 
This does not apply only to these people, rather similar things happened to many people of knowledge and religious commitment. Allaah will accept good deeds from all of His believing slaves, and He will forgive their sins: 
“Our Lord! Forgive us and our brethren who have preceded us in Faith, and put not in our hearts any hatred against those who have believed. Our Lord! You are indeed full of kindness, Most Merciful”
[al-Hashr 59:10]
Undoubtedly those who strive to seek the truth and religion by means of following the Messenger (peace and blessings of Allaah be upon him) will make some mistakes, but Allaah will forgive the mistakes, in answer to the du’aa’ to which Allaah responds from His Prophet and the believers when they say: “Our Lord! Punish us not if we forget or fall into error”[al-Baqarah 2:286]. 
If a person follows his own ideas and whims and desires, and begins to vilify those who differ from him for the mistakes that they make, thinking that he is correct after he tried hard, when in fact it is an innovation that is contrary to the Sunnah, then he has to be consistent, more or less, with those whom he respects among his companions. It is very rare to find anyone among the later scholars who is free of such mistakes, because there is a great deal of confusion and people are further away from the light of Prophethood by which guidance and correction are reached and doubt and confusion are removed. End quote. 
Dar’ Ta’aarud al-‘Aql wa’l-Naql (2/102-103). 
2 – The second principle: If it is known that he basically respects the laws of Allaah and follows His Messenger, both inwardly and outwardly, then his words and deeds should be measured against the standard of the Qur’aan and Sunnah, and his good deeds and bad deeds should be weighed up, along the lines referred to above. 
Shaykh al-Islam (may Allaah have mercy on him) said: 
All of that should be judged according to the general principle that when there are pros and cons, good and bad, or there are many of both, then one should determine which is prevalent. If the pros and cons are many and the good conflicts with the bad, if enjoining good and forbidding evil may achieve some interest and ward off some evil, then we should consider the opposite scenario: if what could be missed of interests or causes of evil is greater, then there is no need to take action and it may even be haraam to do so if the resulting evil will outweigh the benefits of taking action.
But the pros and cons are to be measured by the standard of sharee’ah. If it is possible to follow the texts then one should not turn away from them, but if there is no text then he should try his utmost to examine similar cases (in which the scholars passed judgement), and for the one who knows the texts of sharee’ah and has experience in this field and knows how to derive rulings from them, it is very rare that he would need anything else. 
Based on that, if this person or group has some good practices and some bad practices, and they cannot see the difference between them, rather they will do all of them or abandon all of them, then it is not permissible to enjoin good and forbid evil in this case, rather the situation should be examined: 
If the good practices predominate, then they should be enjoined to do them, even if that means they will also do some bad practices that are less significant. They should not be forbidden to do the bad practices if that will lead to them missing out on some good practices that are more significant. In that case, forbidding it would come under the heading of blocking people from following the way of Allaah and striving to prevent them from obeying Allaah and His Messenger (peace and blessings of Allaah be upon him), and stopping them from doing good deeds! 
But if the bad practices predominate, then they should be forbidden to do them, even if that means that they will miss out on some good practices that are less significant. In this case enjoining what is good may lead to them doing even more bad deeds, and this enjoining becomes like enjoining something evil, and calling people to disobey Allaah and His Messenger! 
But if the good and the bad are of equal significance, then they should neither be enjoined to do both or to stop doing both. In this case, sometimes enjoining good may be right and sometimes forbidding evil may be right, and sometimes neither enjoining good nor forbidding evil may be right, when the good and the bad are of equal measure and cannot be separated. This has to do with some specific cases. 
But with regard to the type of deeds: good should be enjoined at all times and evil should be forbidden at all times. 
With regard to an individual person or group: whatever good they do should be enjoined and praised and whatever evil they do should be forbidden and criticized, provided that enjoining what is good does not lead to missing out on an even greater good or committing an even greater evil, and that forbidding evil does not lead to committing an even greater evil or missing out on an even greater good. 
If the matter is not clear, then the believer should strive until the truth becomes clear to him, and he should not do any good deed except on the basis of knowledge and good intention. If he does not do that he will be sinning, because failing to do an obligatory action is a sin, and doing that which is forbidden is also a sin. This is a very big issue. There is no power and no strength except with Allaah. End quote. 
Al-Istiqaamah (2/216-219) 
Shaykh Ibn Baaz (may Allaah have mercy on him) said in Majmoo’ al-Fataawa (7/311-315): 
Whatever there are of the opinions of some scholars and seekers of knowledge with regard to matters that are subject to ijtihaad, the holder of that opinion is not to be rebuked or blamed if he is qualified to engage in ijtihaad. If someone disagrees with him it is more befitting to debate with him in a proper manner so as to arrive at the truth in the fastest way and so as to ward off the whispers of the shaytaan and avoid inciting hatred among the believers. 
If that (i.e., friendly discussion) is not possible, and someone thinks that he has to highlight some mistakes, then that should be done with the best and gentlest wording and subtle gestures, without attacking, criticizing or going to extremes which may lead to rejecting or turning away from the truth, and without getting personal, making accusations about intentions or saying things for which there is no need. The Messenger (peace and blessings of Allaah be upon him) used to say in such cases: “What is the matter with people who say such and such…” end quote. 
And Allaah knows best. 
The third principle: is that one should discuss only what was actually said, otherwise it will be a lie, as the Prophet (peace and blessings of Allaah be upon him) said to the one who asked him about gheebah (backbiting): 
It was narrated from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do you know what backbiting is?” They said: Allaah and His Messenger know best. He said: “When you say about your brother something that he dislikes.” They said: What if what I say about my brother is true? He said: “If it is true then you have backbitten about him and if it is not true then you have told a grave lie about him.”
Narrated by Muslim (2589). 
Shaykh al-Islam (may Allaah have mercy on him) was asked: 
Is it permissible to speak about one who does not pray, or not? 
He replied: 
If it is said concerning him that he does not pray, and that is indeed the case, then this is permissible, and others should be told about that and he should be shunned until he starts to pray… end quote. 
Athaar Shaykh al-Islam (5/122). 
It should also be noted that in the case of many of these daa’iyahs, their da’wah is primarily aimed at the common Muslims, many of whom may not be praying or may be careless about their prayers, or they may be indulging in sin. For these masses to turn to these daa’iyahs and be attracted by them and be guided at their hands is a very good thing and it is a step forward.  It is not wise to speak to the masses against these daa’iyahs and warn them against them, because many of them have only two choices: either to stay with these daa’iyahs or go back to their old ways, and undoubtedly staying with these daa’iyahs is better for them. 
But what the followers of truth must do is to take care of these daa’iyahs and try to guide them gradually to the way of Ahl al-Sunnah. 
With regard to what you have mentioned about the mistakes of this specific person, which the Muslims should be warned about and be told of where he is going against the Book of Allaah and the Sunnah of His Prophet and the consensus of the Muslims, his way of da’wah should be examined in the light of the general principles of knowledge as mentioned above. If it is possible for one who is knowledgeable, smart and religiously committed to benefit himself and others from what this person and others like him have of goodness, and protect himself and warn others from the errors and innovations that they have, then that is good, in sha Allaah. Otherwise, in that which is purely or mostly good we have sufficient and have no need of him, in sha Allaah. 
And Allaah knows best.