Praise be to Allaah.
It is not essential for the Muslim to follow anyone in the sense that he accepts everything that he says or does, apart from the Messenger of Allaah (peace and blessings of Allaah be upon him). As for anyone other than the Messenger of Allaah (peace and blessings of Allaah be upon him), we may take or leave whatever he says, as Imam Maalik (may Allaah have mercy on him) said: "The words of everyone may be taken or left, apart from the occupant of this grave," and he pointed to the grave of the Prophet (peace and blessings of Allaah be upon him).
With regard to joining some group or other, there is no doubt that Allaah and His Messenger (peace and blessings of Allaah be upon him) have enjoined us to be with the jamaa’ah (main body) of the Muslims.
The Prophet (peace and blessings of Allaah be upon him) said: "The hand of Allaah is with the jamaa’ah." [Narrated by al-Tirmidhi 2167 and classed as saheeh by al-Albaani]
And he said: "You must stay with the jamaa’ah, for the wolf eats the sheep that wanders off alone." [Narrated by al-Nasaa’i, 847 and classed as hasan by al-Albaani in Saheeh al-Nasaa’i]
And he said: "The Shaytaan is with one, but he is further away from two." [Narrated by al-Tirmidhi, 2165; classed as saheeh by al-Albaani in Saheeh al-Tirmidhi. And there are many ahaadeeth on this topic]
Undoubtedly it is prescribed for the Muslim to cooperate with a group of his brothers in obeying Allaah and His Messenger (peace and blessings of Allaah be upon him) with regard to matters such as enjoining what is good and forbidding what is evil, calling others to Allaah, seeking knowledge and encouraging one another to adhere to the truth and be patient, etc. In this manner a person can protect himself against the Shaytaan as indicated in the ahaadeeth quoted above. This is included in the words of Allaah (interpretation of the meaning):
"By Al-'Asr (the time). Verily, man is in loss, Except those who believe (in Islamic Monotheism) and do righteous good deeds, and recommend one another to the truth, and recommend one another to patience." [al-'Asr 103:1-3]
But if what the questioner means is joining a group in the sense of thinking that this is the only group that is following the truth and that all others are following falsehood, loving those who follow this group with him and hating others – as happens with many of those who are members of these groups nowadays, then this is a kind of injustice which Allaah and His Messenger, and the believers, do not like, and which only makes the ummah more fragmented and weak. Rather the believers love all the believers, as Allaah says (interpretation of the meaning):
"Verily, your Wali (Protector or Helper) is none other than Allaah, His Messenger, and the believers." [al-Maa’idah 5:55]
"The believers are nothing else than brothers (in Islamic religion)." [al-Hujuraat 49:10]
And the Prophet (peace and blessings of Allaah be upon him) said: "The Muslim is the brother of his fellow Muslim." All of these groups which are agreed upon the bases of Ahl al-Sunnah wa’l-Jamaa’ah are defending Islam one way or another. No one group has a monopoly on the truth, and the call to Allaah (da’wah) needs the efforts of all of them and more.
The believer loves and supports all the believers and cooperates with them in obeying Allaah, even if they are far away from him, and he refrains from helping them to disobey Allaah, even if they are the closest of people to him.
Shaykh Ibn Baaz (may Allaah have mercy on him was asked about the ruling on joining Islamic groups and following the methodology of a particular group and not others. He replied:
It is obligatory on every person to adhere to the truth, what Allaah and His Messenger (peace and blessings of Allaah be upon him) said, not to adhere to the methodology of any group, whether it is the Ikhwan al-Muslimeen or Ansaar al-Sunnah or any other group. He should adhere to the truth. If he joins the Ansaar al-Sunnah and helps them with regard matters in which they are following to the truth, or he joins the Ikhwaan al-Muslimeen and agrees with them on matters in which they are following the truth, without going to extremes or being negligent, there is nothing wrong with that. But if he adheres to their set of beliefs and never deviates from it, this is not permitted. He has to follow the truth wherever it leads him. If the truth is with the Ikhwaan al-Muslimeen, he has to follow it, and if it is with the Ansaar al-Sunnah, he has to follow it, and if it is with another group, he has to follow it. He has to follow the truth, and help all other groups with regard to the truth, but he should not adhere to a particular way of thinking never forsaking it even if it turns out to be false or mistaken. That is wrong, and is not permitted. He should be with the group in every way in which they are correct, and not with them in the matters in which they are wrong.
[Majmoo’ Fataawa wa Maqaalaat Mutanaawi’ah li Samaahat al-Shaykh al-'Allaamah 'Abd al-'Azeez ibn Baaz (may Allaah have mercy on him), p. 237.]