Bidah

In Islam, Bid‘ah (Arabic: بدعة‎‎; English: innovation) refers to innovation in religious matters. Linguistically the term means "innovation, novelty, heretical doctrine, heresy".

In classical Arabic literature (adab), it has been used as a form of praise for outstanding compositions of prose and poetry.

In early Islamic history, bid'ah referred primarily to heterodox doctrines (as evidenced below). However, in Islamic law, when used without qualification, bid'ah denotes any newly invented matter that is without precedent and is in opposition to the Qur'an and Sunnah.

Scholars (most prominent of which is Imam Shafi‘i) generally have divided bid'ah into two types: innovations in worldly matters and innovations in religious matters. Some have additionally divided bid'ah into lawful and unlawful innovations, the details of which are discussed below.

Introducing and acting upon a bid‘ah in religious matters is a sin and considered one of the enormities in Islam that is obligatory to immediately desist and repent from.

Some Sunni Muslim scholars have divided bid‘ah in worldly matters into two types:

There are a number of different definitions of Bid‘ah.

The Qur’anic verse: "This day I have perfected your religion for you, completed my favor upon you, and have chosen for you Islam as your religion."(Quran 5:4), is considered by at least some Muslim to be against bid'ah in religion. The Sunnah has many more prohibitions against innovation in religion.

Ali ibn Abu Talib, of the Rashidun (rightly guided Caliphs), said; "He who innovates or gives protection to an innovator, there is a curse of Allah and that of His angels and that of the whole humanity upon him."`Abd Allah ibn `Umar said: "Every innovation is misguidance, even if the people see it as something good."

...
Wikipedia