Imaam Ibn Qayyim (rahimahullaah Ta’aala) said:
If bid’ah only consisted of lies, then it would NOT have been accepted and everybody would even hurry to condemn it and refute it. And if it only consisted of Haqq (truth), then it would not have been a Bid’ah, rather, in agreement with the Sunnah. But it (Bid’ah) consists of both truth and lies in which the truth is clothed with lies.
[as-Sawaa´iq al-Mursalah (3/925)]
Do Not Be Deceived By Ahlul-Bid’ah who may agree with the Salafees in certain matters
Adh-Dhahabee (rahimahullaah) said:
“If you see the innovative mutakallim saying: ‘leave out the Qur’aan and Sunnah and bring forth logic‘, then know that he is Aboo Jahl.
And if you see the ‘One on the Spiritual Path’, [who claims that by practicing a set of prescribed forms of innovated worship he will attain oneness with Allaah] (i.e. the Soofees) saying: ‘Leave us from [knowledge] that is transmitted (i.e. the Qur’aan and Sunnah) and bring forth the ‘Taste and Ecstasy of Passion’(1),‘ then know that he is Ibless (Shaytaan) become manifest in human form, or has become incarnate within him; so if you become cowardly then run away from him, otherwise wrestle him down, and sit on his chest with your knee, and read ayaatul-kursee, and strangle him.”
(1) The taste and ecstasy of passion is that which they claim to achieve after the continual performance of innovated forms of dhikr.