Shaikh Abdullaah Al-Bukhaari (may Allaah preserve him) says:

And from the greatest of affairs in preserving and upholding this Shariah, is to stand firm with knowledge and justice against bidah and the innovators–utilising the paths of the Shariah to oppose their transgressions; repel their plots; manifest the signpost of (sound) allegiance and enmity (for the sake of Allaah); love and hate for the sake of Allaah and putting it into practice.

If the harm of innovation (i.e. in religion) was limited to the innovator and not transferred to others, then the affair would have come to an end and the circumstances would have been made easy. However there is what harms the innovator and there is what harms his followers with regards to following bidah. There is what harms the Religion itself and there is what harms the Ummah that falls into bidah in its religious affairs.

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[Source: At-Ta’aqqubaat As-Sareehah Alaa Risaalah An-Naseehah Lid-Duktoor Ibraaheem Ibn Aamir Ar-Ruhayli. Page: 56-58. Slightly paraphrased]

Abu Mu’aawiyah (Abdullaah Al-Gambi)