Bid'ah (Arabic: بدعه ) is an Islamic term meaning innovation of religious beliefs or worship. Linguistically, bid'ah means "innovation". Islamically speaking, bid'ah refers to religious innovation, for example, religious practices that were not advocated by Muhammad.
The role of bid'ah is a hotly debated topic among Muslim scholars. Many Sunni Muslims consider it to be a violation of fundamental Islamic principles, and thus those who engage in bidah are accused of practicing heresy. They base this in part on an authenic hadith recorded in Al-Bukhari and Al-Muslim, in which Aisha reported Muhammad said, "Whoever innovates into this affair of ours (Islam) something that we have not commanded it is to be rejected." Another is: "Every innovation is misguidance and every misguidance is in the hellfire." But most Sunni differentiate between an innovation of misguidance and an innovation of guidance. Such beneficial innovation is known as "Bid'a hasana" which means "good innovation". The good innovations are those innovations that comply with the Qur'an and the narrations (known as Hadith) of Muhammad, whereas the bad innovations or 'innovations of misguidance' are those innovations that do not comply with the Qur'an and the narrations of Muhammad. Every innovation created by the people of knowledge that complies with the Qur'an and acceptable hadith is a good innovation, as indicated by the following authentic hadith of Muhammad narrated by Muslim:
One example of a good innovation is that which was done by Yahya Ibn Ya^mar--adding the dots above and below some of the Arabic letters in the Qur'an. Those who originally wrote down the revelation believed to have been revealed to Muhammad, wrote the verses of the Qur'an without the diacritical marks that are present today in the Arabic letters. For example, the letter ba' (Arabic: ب ) was written without a dot underneath; the letter ta' (Arabic: ت ) was written without two dots on top; and the letter tha' (Arabic: ث ) was written without three dots above. The entire Qur'an was written without these dots over or under the letters. Adding the dots took place after the death of Muhammad within a certain period of time. This is classified as a "good bida" as it is in no violation of any Islamic teachings or juristic principles and aids Muslims in reading the scripture. Another example of a good bid'ah, which is very common, is saying (Arabic: صدق الله العظيم ): "Allah (God) said the truth", at the end of the recital of any part of the Qur'an. It is assumed that Allah tells nothing but the truth, but nowhere in the Qur'an does a chapter sura end with "Allah (God) said the truth".