A lot of Muslim youths are asking about the ruling on joining Islamic groups and adhering exclusively to the methodology of a particular group.
Praise be to Allaah.
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 Allah have mercy on him), p. 237