Bidʿa (Arabic: البدعة, lit: innovation) is adding something to, or omitting something from, religion. Bid'a stands in contrast to sunna (i.e., a practice or belief that is mentioned in the Qur'an or hadiths). In the Islamic tradition, bid'a is considered as an instance of disbelief or polytheism.
There is disagreement among Muslims as to the instances of innovation in religion, and each group accuses the others of innovation. Among Muslim scholars, Ibn Taymiyya is said to have made such accusations more than anyone. All Shiite and Sunni jurists consider bid'a forbidden.
In the Shiite view, takattuf (placing one hand on the other during prayer), the congregational Tarawih prayer, saying "amin" in prayer after the recitation of al-Fatiha are among the instances of bid'a.
Some Sunni scholars believe that bid'a is divided into good bid'a (such as performing Tarawih prayer congregationally, which was innovated by Umar b. al-Khattab) and wrong bid'a. However, other Sunni scholars hold that all kinds of innovation in religion are wrong and forbidden.
Among the important works on bid'a are al-I'tisam by Abu Ishaq Ibrahim Shatibi al-Shatibi amd al-Bid'a by Ayatollah Ja'far Subhani.
Definitions of Bid'a
Muslim scholars have given various definitions for bid'a. In Ayatollah Subhani's al-Bid'a, twenty-two definitions by Shiite and Sunni scholars are reported. For instance, Ibn Hajar al-Asqalani defines bid'a the opposite of sunna, and al-Sharif al-Murtada defines it as any addition or omission in religion. The jurists consider bid'a as adding something to religion which does not belong to it, such as regarding an act of worship which is not part of religion as a ritual prescribed by religion; according to jurists, even to regard such an act as recommended is an instance of bid'a.  In a more comprehensive definition, al-Allama al-Majlisi considers bid'a as emergence of an act or belief in religion after the Prophet (s) which is either prohibited, not found in the tradition, or not coming under a more general religious ruling.
Bid'a is used as opposed to sunna (i.e., the doctrines and practices that are found in the Qur'an and hadiths); it can occur in the domain of religious beliefs or rulings. 
Bid'a, a Grave Sin
In Sunni and Shiite sources, many hadiths can be found that criticize and condemn bid'a; for instance, according to a hadith in the Musnad of Ahmad b. Hanbal and Sunan of Ibn Maja, the Prophet (s) announced all types of bid'a as error. Ibn Maja also reports that the Prophet (s) stated that the fasts, prayers, alms, hajj, umra, and jihad of the innovators will not be accepted. 
In Shiite sources, it is reported in al-Kafi that all kinds of bid'a are error, and all error is doomed to hell. Al-Shaykh al-Saduq also reports the hadiths related to bid'a in his Man la yahduruh al-faqih, in the section on grave sins. According to a hadith he reports, Imam al-Baqir (a) counted bid'a as an instance of disbelief and polytheism. Based on this and other evidence, Ayatollah Ja'far Subhani, among others, considers bid'a a grave sin. 
Criticism of Bid'a in the Qur'an
Qur'an 57:27 states that God did not legislate monasticism for Christians, and that it was an innovation that they made. According to Qur'an 16:116, no one is allowed to make something permissible (halal) or forbidden (haram) on his own and falsely attribute a ruling to God. Allama Tabatabai mentions that the context of this verse indicates that believers are prohibited from innovation in religion.
According to jurists, anything that is an instance of bid'a is forbidden. For instance, as to how a witness may take an oath in the court, al-Muhaqqiq al-Hilli states that swearing by anything other than God's name, such as by sacred books or the names of the Prophet (s) or Imams (a), is not allowed, because this is bid'a. In Jawahir al-kalam, it is reported that Twelver Shiite jurists consider washing the face or hands for the third time in wudu a bid'a and thus forbidden.
Widespread Accusations of Bid'a
Muslims have constantly disagreed as to which actions or beliefs are bid'a. As Averroes states, each Muslim sect accuses the others of bid'a; for instance, Wahhabis consider Muslim philosophers, Shiites, Mu'tazilites, Ash'arites, and Kharijites innovators, and Ash'arites regard as innovators Mu'tazilites, Shiites, and Batinis. Ibn Taymiyya is said to have accused others of bid'a more than any other Muslim scholar. He regarded any act or belief whose basis he could not find in the Qur'an or the sunna of the Prophet (s) or Companions as bid'a. 
Among the practices that are considered by Twelver Shiites to be bid'a are takattuf (placing one hand on the other during prayer), the congregational Tarawih prayer, saying "amin" in prayer after the recitation of al-Fatiha, and divorcing one's wife three times in one session.
"Good" and Wrong Bid'a
Some Sunni scholars, such as al-Shafi'i, Ibn Hazm, al-Ghazali, and Ibn Athir maintain that every bid'a is not wrong and that there are "good" instances of bid'a. The basis for this view is Umar b. al-Khattab's innovation of performing recommended prayers of the month of Ramadan congregationally. Umar called this innovation a "good bid'a". In this regard, al-Ghazali writes that only the bid'a that is against sunna is forbidden. Accordingly, some Sunni scholars have stated that bid'a can be divided, based on its ruling, into five types: obligatory, forbidden, recommended, reprehensible, and permissible.
Most Shiite scholars and some Sunni scholars reject this division. Adducing the hadith that states, "All bid'a is error", al-Allama al-Majlisi rejects the division of bid'a into five types and considers all types of bid'a forbidden. Among Sunni scholars, al-Shatibi disagreed with this division. His first objection was that there is no religious evidence for this division, and hence the division itself is a bid'a. His second objection is that the concept of an obligatory, recommended, or permissible innovation contains a paradox, because if there is any evidence that something is obligatory, recommended, or permissible in religion, it will not be a bid'a.
According to a prophetic hadith, innovators are to be "slandered/defamed" ("bahituhum"). Scholars disagree as to the precise meaning of the hadith. Some maintain that it indicates the permission of slandering the people of bid'a, whereas others hold that since lying is forbidden, defaming innovators through false accusations is not allowed. A third group have suggested that the word "bahituhum" simply means "confound them" by solid proofs against their claims.
Works on Bid'a
Muslim scholars have written many books and treatises on bid'a, some of which are as follows:
- Al-Bida' wa al-nahy anhā, by Ibn Waḍḍah al-Qurtubi
- Al-Hawādith wa l-bida', by Tartushi
- Al-Bā'ith, by Abu Shama
- Al-I'tisām, by Abu Ishaq Ibrahim Shatibi
- Al-Bida', by al-muhdatha, by Abu-l Qasim Kufi
- Al-Bida', by Ja'far Bagheri
- Subḥānī Tabrīzī, al-Bidʿa, p. 25- 30.
- Ṭabāṭabāʾī, Rīyāḍ al-masāʾil, vol. 8, p. 175; Khoeī, Ṣirāṭ al-najāt, vol. 3, p. 428.
- Khoeī, Ṣirāṭ al-najāt, vol. 3, p. 428.
- Khoeī, Mawsūʿat al-Imām al-Khūʾī, vol. 6, p. 355.
- Majlisī, Biḥār al-anwār, vol. 71, p. 202, 203.
- Shāhrūdī, Farhang-i fiqh, p. 75.
- Narāqī, ʿAwāʾid al-ayyām, p. 319.
- Narāqī, ʿAwāʾid al-ayyām, p. 319; Khoeī, Mawsūʿat al-Imām al-Khūʾī, vol. 6, p. 355.
- Subḥānī Tabrīzī, al-Bidʿa, p. 15- 21.
- Kulaynī, al-Kāfī, vol. 1, p. 56.
- Ṣadūq, Man lā yaḥḍuruh al-faqīh, vol. 3, p. 572.
- Subḥānī Tabrīzī, al-Bidʿa, p. 5.
- Subḥānī Tabrīzī, al-Bidʿa, p. 13- 15.
- Ṭabāṭabāʾī, al-Mīzān, vol. 12, p. 365.
- Subḥānī Tabrīzī, al-Bidʿa, p. 13, 14.
- Ṭabāṭabāʾī, al-Mīzān, vol. 12, p. 365; vol. 19, p. 173.
- Narāqī, ʿAwāʾid al-ayyām, p. 319.
- Muḥaqiq Ḥillī, al-Nihāya, vol. 2, p. 78.
- Najafī, Jawāhir al-kalām, vol. 2, p. 276.
- Narāqī, ʿAwāʾid al-ayyām, p. 319.
- Gudhashta, Bidʿat, p. 560- 561.
- Ṭārimī, Bidʿat, p. 517.
- Subḥānī Tabrīzī, al-Bidʿa, p. 160, 161, 179.
- Pākatchī, Bidʿa, p. 566.
- Subḥānī Tabrīzī, al-Bidʿa, p. 119, 199, 200.
- Subḥānī Tabrīzī, al-Bidʿa, p. 26, 27.
- Subḥānī Tabrīzī, al-Bidʿa, p. 26, 27; Ṭabasī, Dirāsat fiqhīyya, 168.
- Ṭabasī, Dirāsat fiqhīyya, 168.
- Ghazālī, Iḥyāʾ ʿulūm, vol. 2, p. 4, 5.
- Shāṭibī, al-Iʿtiṣām, vol. 1, p. 241- 245.
- Shahīd al-Awwal, al-Qawā'id wa al-fawāʾid, vol. 2, p. 144- 146.
- Majlisī, Mir'āt al-'uqūl, vol. 1, p. 193.
- Shāṭibī, al-Iʿtiṣām, vol. 1, p. 246.
- Kulaynī, al-Kāfī, vol. 2, p. 375.
- Khoeī, Miṣbāḥ al-fiqāha, vol. 1, p. 281; Gulpāyigānī, al-Durr al-manḍud, vol. 1, p. 149.
- Ṭabāṭabāʾī, Rīyāḍ al-masāʾil, vol. 16, p. 42.
- Fayḍ al-Kāshānī, al-Wāfī, vol. 1, p. 245; ( Fatwa of 5 Maraji' Taqlid about lying and slander (Persian)).
- Subḥānī Tabrīzī, al-Bidʿa, p. 9.
- Fayḍ al-Kāshānī, Muḥsin. Kitāb al-Wāfī. 1st edition. Edited by Ḍīyāʾ al-Dīn Ḥusaynī Iṣfahānī. Isfahan: Kitabkhāna-yi Amīr al-Muʾminīn, 1406 AH.
- Ghazālī, Muḥammad. Iḥyāʾ ʿulūm al-dīn. 1st edition. Beirut: Dār al-Fikr1406 AH.
- Gudhashta, Nasir. Bidʿat, Dāʾirat al-maʿārif buzurg-i Islāmī. Tehran: Makaz-i Dāʾirat al-maʿārif buzurg-i Islāmī, 1381 Sh.
- Gulpāyigānī, Sayyid Muḥammad Raḍī. Al-Durr al-manḍud fī aḥkām ḥudud. 1st edition. Qom: Dār al-Qurʾān al-Karīm, 1412 AH.
- Khoeī, Sayyid Abū l-Qāsim al-. Ṣirāṭ al-najāt. Edited by Musā Mufīd al-Dīn Āṣī Āmilī. 1st edition. Qom: Maktab Nashr al-Muntakhab, 1416 AH.
- Khoeī, Sayyid Abū l-Qāsim al-. Mawsūʿat al-Imām al-Khūʾī. First edition. Qom: Muʾassisa Ihyāʾ Āthar al-Imām al-Khūʾī, 1418 AH.
- Khoeī, Sayyid Abū l-Qāsim al-. Miṣbāḥ al-fiqāha. Taqrīr-i Mīrzā Muḥammad ʿAlī Tawhīdī. 4th edition. Qom: Anṣārīyān, 1417 AH.
- Kulaynī, Muḥammad b. Yaʿqūb al-. Al-Kāfī. Tehran: Dār al-Kutub al-Islāmiyya, 1407 AH.
- Majlisī, Muḥammad Bāqir al-. Biḥār al-anwār. Second edition. Beirut: Dār Iḥyāʾ al-Turāth al-ʿArabī, 1403 AH.
- Majlisī, Muḥammad Bāqir al-. Mir'āt al-'uqūl. Edited by Rasūlī Maḥallātī. Tehran: Dār al-Kutub al-Islāmiyya, 1404 AH.
- Muḥaqiq Ḥillī, Jaʿfar Ḥasan. Al-Nihāya wa Nukatihā. 1st edition. Edited by: Gurūh-i pajūhish-i Daftar-i Intishārāt-i Islāmī. Qom: Daftar-i Intishārāt-i Islāmī affiliated to Jāmiʿa-yi Mudarrisīn-i Ḥawza-yi ʿIlmīyya-yi Qom, 1412 AH.
- Najafī, Muḥammad al-Ḥasan al-. Jawāhir al-kalām fī sharḥ sharāʾiʿ al-Islām. Seventh edition. Edited by ʿAbbās Qūchānī & ʿAlī Ākhūndī. Beirut: Dār Iḥyāʾ al-Turāth al-ʿArabī, [nd].
- Narāqī, Aḥmad. ʿAwāʾid al-ayyām fī bayān qawāʿid al-aḥkām wa muhimmāt masāʾil al-ḥalāl wa l-ḥarām. 1st edition. Qom: Daftar-i Tablīghāt-i Islāmī-yi Ḥawza-yi Ilmīya-yi Qom, 1417 AH.
- Pākatchī, Aḥmad. Bidʿa; Barrasī-yi tārīkhī.1st edition. Tehran: Makaz-i Dāʾirat al-maʿārif buzurg-i Islāmī, 1381 Sh.
- Ṣadūq, Muḥammad b. ʿAlī al-. Man lā yaḥḍuruh al-faqīh. Edited by ʿAlī Akbar Ghaffārī. Qom: Intishārāt-i Islāmī, 1413 AH.
- Shahīd al-Awwal, Muḥammad b. Makkī. Al-Qawā'id wa al-fawāʾid. Edited by: Sayyid ʿAbd al-Hādī Ḥakīm. Qom: Kitābfurūshī-yi Mufīd, 1400 AH.
- Shāṭibī, Ibrāhim b. Mūsā.Al-Iʿtiṣām. Edited by Sālim b. ʿIyd al-Hilālī. 1st edition. Riyadh: Dār Ibn ʿAfan, 1412 AH.
- Subḥānī Tabrīzī, Jaʿfar. Al-Bidʿa; Mafhūmuhā, ḥadduhā. Qom: Muʾassisat Imām al-Ṣādiq, 1416 AH.
- Ṭabasī, Najm al-Dīn. Dirāsat fiqhīyya fī masāʾil khilāfīyya. Qom: Daftar-i Intishārāt-i Islāmī, 1429 AH.
- Ṭabāṭabāʾī, ʿAlī. Rīyāḍ al-masāʾil fī taḥqīq al-aḥkām bi-dalāʾil. Edited by Muḥammad Bahramand/Muḥsin Qadīrī. 1st edition. Qom: Muʾassisat Āl al-Bayt, 1418 AH.
- Ṭabāṭabāʾī, Sayyid Muḥammad Ḥusayn al-. Al-Mīzān fī tafsīr al-Qurʾān. Qom: Daftar-i Intishārāt-i Islāmī, 1417 AH.
- Ṭārimī, Ḥasan. Bidʿat. Dānishnāma-yi jahān-i Islām. 2st edition. Tehran: Bunyād-i Dāʾirat al-Maʿārif al-Islāmī, 1375 AH.
- Shāhrūdī, Sayyid Maḥmūd. Farhang-i fiqh muṭābiq bā madhhab-i Ahl al-Bayt. Second edition. Qom: Muʾassisat Dāʾirat al-Maʿārif al-Fiqh al-Islāmī, 1388 Sh.
- فتوای ۵ مرجع تقلید درباره دروغ گفتن و بهتان زدن ( Fatwa of 5 Maraji' Taqlid about lying and slander (Persian)). Accessed: 2023/10/21.