What is the ruling on Bid‘ah (religious innovation) and the person who does Bid‘ah?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

Innovations in religion are impermissible. The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said that every Bid‘ah (religious innovation) leads to going astray. [Muslim]

The repentance of a person who does Bid‘ah is not accepted until he stops doing the Bid‘ah. The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said that Allaah The Almighty does not accept the repentance of a person who does Bid‘ah until he stops doing the Bid‘ah. [At-Tabaraani in Al-Kabeer] Al-Albaani graded this Hadeeth as Saheeh (Authentic).

The ruling that applies to the person who does Bid‘ah differs according to the type of Bid‘ah he does and whether or not it results in disbelief, in order to know how to deal with such a person and the ruling on the permissibility of praying behind (when he is leading the congregational prayer) and whether or not to abandon this person.

Allaah Knows best.