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]