Fitra, or fitrah (Arabic: فطرة / ALA-LC: fiṭrah), is an Arabic word meaning ‘disposition’, ‘nature’, ‘constitution’, or ‘instinct’. In a mystical context, it can connote intuition or insight. It 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.
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 
- To split or cleave
- Implies opening up and coming out
- Verb means 'to bring forth', 'to originate', 'to knead and shape dough'.
Sunan al-Fitra 
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. 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, II.502) 
- Further discussion of the medical implications of fitrah can be found at: http://omarkasule-03.tripod.com/id702.html
- USC Center for Muslim-Jewish Engagement Compendium of Islamic Texts, retr. 13 Jul. 2012: http://www.cmje.org/religious-texts/hadith/muslim/002-smt.php
Further reading 
- 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