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Fitra, or fitra (Arabic: فطرة / ALA-LC: fiṭrah), is an Arabic word that has no exact English equivalent although it has been translated as 'primordial human nature', and as "instinct" or common sense ('urf). It has also been suggested  that a close approximation, in terms of Western philosophy, is Kant's concept of 'ought'. In a mystical context, it can connote intuition or insight and is similar to the Calvinist term Sensus divinitatis.
According to Islamic theology, human beings are born with an innate inclination of tawhid (Oneness), which is encapsulated in the fitra along with compassion, intelligence, ihsan and all other attributes that embody what it is to be human. It is for this reason that some Muslims prefer to refer to those who embrace Islam as reverts rather than converts, as it is believed they are returning to a perceived pure state.  The perfect embodiments of fitra were Abraham and Muhammad.
So set thy face to the service of religion as one devoted to God. And follow the nature made by Allah (fitratallāhi) – the nature in which He has fashioned all mankind (fatarannāsa ilayha). There is no altering the creation of Allah. That is the right religion but most men know not. (30:30)
Allah's Apostle said, "No child is born except on the fitra and then his parents make him Jewish, Christian or Magian (Zoroastrian), as an animal produces a perfect young animal: do you see any part of its body amputated?"
- Sahih al-Bukhari, Volume 2, Book 23, Number 441
Root of word
- The root verb means to split or cleave
- Implies opening up and coming out
- The term Fitra means 'to bring forth', 'to originate', 'to knead and shape dough'.
Fitra has a physical component as well as a spiritual one. The fitra of the human body is its beauty and perfection as created by God. Although created perfectly by God, humans are permitted to enhance their appearance through means approved by God, such as clothes, bathing and perfumes. These are changes to surface appearance, but not to one's essential fitra.
However, radical changes to one's body to suit personal taste or social fashion are condemned as unlawful changes to fitra. Based on this reasoning, and based on several verses in the Qur'an (e.g. 32:6-7, 31:20), stating that Allah created humans perfectly. Procedures to remove or hide deformities resulting from disease or injury are seen as restoring fitra, rather than changing it, and are therefore allowed.
The sunan al-fitra (lit., "customs of nature") are a collection of hygienic or cosmetic practices enjoined by Muhammad as consistent with fitra:
'A'isha reported: Muhammad said: Ten are the acts according to fitra: clipping the mustache, letting the beard grow, using the tooth-stick, snuffing water in the nose, cutting the nails, washing the finger joints, plucking the hair under the armpits, shaving the pubic hair and cleaning one's private parts with water. The narrator said: I have forgotten the tenth, but it may have been rinsing the mouth. (Sahih Muslim, 261a) 
Circumcision has not been included and is supposed to be the fitra which the narrator forgot. "Five things are part of the fitrah: circumcision, removing the pubic hair, trimming the moustache, cutting the nails, and plucking the armpit hair." (Reported by al-Bukhari, 5441.)
- Abu al-Fazl Izzati, Islam and Natural Law, Islamic College for Advanced Studies Press, 2002, pp.93f. ISBN 1904063055
- Frederick M. Denny, God's Friends: The Sanctity of Persons in Islam, in R. Kieckhefer and G. Bond (editors). Sainthood: Its Manifestations in World Religions, University of California Press, 1990. ISBN 9780520071896
- Abu al-Fazl Izzati, Islam and Natural Law, Islamic College for Advanced Studies Press, 2002, p.96. ISBN 1904063055
- John Silber, Kant's Ethics: The Good, Freedom, and the Will, Mouton de Gruyter, 2012, pp. 188ff. ISBN 9781614510710
- Tuba Boz, Religious Conversion, Models and Paradigms, Epiphany: Journal of Transdisciplinary Studies, 2011, pp. 130
- Further discussion of the medical implications of fitrah can be found at: http://omarkasule-03.tripod.com/id702.html
- Sahih Muslim 261a http://sunnah.com/muslim/2/71
- J.M. Cowan (1994), The Hans Wehr Dictionary of Modern Written Arabic
- John Esposito (2003), The Oxford Dictionary of Islam
- M. Masud (1996), Islamic Legal Interpretation: Muftis and Their Fatwas
- Imam Ali, Nahjul Balagha: Sermons, Letters & Sayings of Imam Ali
- Al-Kulayni, al-Usul mina ‘l-Kãfi, vol. 2, p. 13; al-Bukhãri, Sahih, vol. 2 (Beirut: Dãr al-Fikr, 1401) p. 104