Shaykh Mashhoor states:

“If a man, in regards to an issue, has a view which is contrary to that held by Ahlul Hadeeth, then it is not suitable to expel him from the realm of Ahlul Hadeeth except in one of the three cases:

1) If he opposes something from the Usool (foundations/principles) of Ahlul Hadeeth. Like for example if he adheres to ta’assub (fanaticism) or tamadhhub (madhhab bigotry) or he does not view the authority of the statements of the Companions.

2) This his erros are many, severe and vile all on account of his corrupt Usool.

3) That he shares with Ahlul Bid’ah an issue which has become a main symbol of them.”

[Taken from “The Madhhab Of Ahlul Hadeeth” p. 81]