Shaikhul Islaam Ibn Taymiyyah [rahimahullaah] said:
The legislated divine law is nourishment for the hearts, so when the hearts are nourished with bidah, giving preference to the Sunnan does not remain in them; then [the affair] becomes like [the situation of a person] who nourishes himself with filth.
[Iqtidaa Siraat Al-Mustaqeem: 1/281. Slightly paraphrased]
Al -Allaamah Zayd bin Muhammad Al-Madkhalee (may Allaah have mercy on him) said:
“There is no doubt that the vile descriptions uttered by the people of innovation- past and present- which they apply to ahlus sunnah is dictated to them by [their] vain desires, shaytaan and the soul that is inclined to evil.”
At-Ta’leeq al-Mateen ‘alaa Kitaab Usool as-Sita wa I’tiqaad ar-Raaziyayn 176
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The questioner says—may Allah reward you with good:
‘There is a person who praises the people of innovation and rejects the speech of the scholars of the Sunnah concerning them, and he also defames the scholars of the Sunnah and so on.’
Shaykh Muhammad ibn Hadi:
“Whoever praises the people of innovation, without doubt, he is from the innovators; rather, he is without doubt from their callers. The people asked our Shaykh—may Allah’s Mercy be upon him—Shaykh ‘Abd al-’Aziz ibn Baz, during the lesson of the explanation of the book Fadl al-Islam is the person who praises the people of innovation considered from them. He said, yes, there is no doubt that he is from them; rather, he is from their callers. This is available in his voice and in writing, all praise is for Allah, and there is no doubt concerning this.”
See: http://ar.miraath.net/fatwah/3909
Translated by Abul Hasan Maalik Al Akhdar