In Islamic law, takfir or takfeer (Arabic: تكفير‎ takfīr) refers to the practice of one Muslim declaring another Muslim an unbeliever or kafir (pl. kuffār). The act which precipitates takfir is termed the mukaffir.

This declaration may be made if the alleged Muslim declares himself a kafir, but more typically applies to a judgement that an action or statement by the alleged Muslim indicates his knowing abandonment of Islam. The sentence for apostasy (irtidad) under Sharia is traditionally interpreted as execution but alternately might be amputation or expulsion.

For this reason orthodox Islamic law normally requires extremely stringent evidence for such accusations. In many cases an Islamic court or a religious leader, an alim must pronounce a fatwa (legal judgement) of takfir against an individual or group.

There are disputes among different schools of religious thought as to what constitutes sufficient justification for declaring takfir. The orthodox Sunni position is that sins generally do not prove that someone is not a Muslim, but denials of fundamental religious principles do. Thus a murderer, for instance, may still be a Muslim, but someone who denies that murder is a sin is a kafir if he is aware that murder is considered a sin in Islam.

Hamza Yusuf Hanson is an American Islamic scholar, and (with Zaid Shakir and Hatem Bazian) is co-founder of Zaytuna College in Berkeley, California, United States. He is a convert to Islam, and is one of the signatories of A Common Word Between Us and You, an open letter by Islamic scholars to Christian leaders, calling for peace and understanding. He has described the 9/11 attacks as "an act of 'mass murder, pure and simple'". Condemning the attacks, he has also stated "Islam was hijacked ... on that plane as an innocent victim".The Guardian newspaper in the United Kingdom reported that he "is arguably the west's most influential Islamic scholar" and added that "many Muslims find his views hard to stomach."

Hamza Yusuf was born to two academics in Washington State and raised in Northern California. In 1977, he became Muslim and subsequently traveled to the Muslim world and studied for ten years in the United Arab Emirates, Saudi Arabia, as well as North and West Africa. Hamza Yusuf spent four years studying in the United Arab Emirates and elsewhere in the Middle East. Later he traveled to West Africa and studied in Mauritania, Medina, Algeria, and Morocco under such scholars as Murabit al Haaj; Baya bin Salik, head of the Islamic court in Al-'Ain, United Arab Emirates; Muhammad Shaybani, Mufti of Abu Dhabi; Hamad al-Wali; and Muhammad al-Fatrati of Al Azhar University in Cairo, Egypt.^{[citation needed]} After more than a decade abroad, he returned to the United States and earned degrees in nursing from Imperial Valley College and religious studies at San José State University.^{[citation needed]}

Abu Dujana Simak bin Kharasha (died 632) was a sahaba and a skilled swordsman who is mentioned in Hadith narrations from the six major Hadith collections of Sunni Islam.

Abu Dujana is remembered as being one of Prophet Muhammad most skilled companions in the battlefield, highly excelling in melee combat. He frequently distinguishing himself in battle by wearing a red band on his head, and engaged in bravado before fighting by strutting in front of his adversaries. In the Battle of Uhud, Prophet Muhammad gave Abu Dujana his sword as the often cited hadith narration reads:

During the Battle of Uhud, Abu Dujana pierced into the enemy's lines, and even came within striking distance to the notorious Quraish leader, Hind bint Utbah who was encouraging others to mutilate the body of dead Muslims. According to various accounts, Abu Dujana spared her since he did not want to stain Muhammad's sword with the blood of a woman.

Abu Dujana, during the Battle of Uhud, received several wounds in his back after placing himself around Prophet Muhammad so as to act as a protection from arrows.

Ibn ʿArabī (Arabic: ابن عربي‎) (Murcia July 28, 1165 – Damascus November 10, 1240) was an Arab Andalusian Sufi mystic and philosopher.

He was sometimes referred to as "the Son of Plato" (Ibn Aflatun) for his devotion to Plato.

'Abū 'Abdillāh Muḥammad ibn 'Alī ibn Muḥammad ibn `Arabī (أبو عبد الله محمد ابن علي ابن محمد ابن عربي ) was born into a respectable family in Murcia, Taifa of Murcia on the 17th of Ramaḍān 561 AH (27th or 28 July 1165 AD). Muḥyiddin Muḥammad ibn ‘Alī ibn Muḥammad ibn ‘Arabī was widely known as al-Shaykh al-Akbar; in medieval Europe he was called Doctor Maximus.

His father, ‘Ali ibn Muḥammad, served in the Army of ibn Mardanīsh. When ibn Mardanīsh died in 1172 AD, ‘Ali ibn Muḥammad swiftly shifted his allegiance to the Almohad Sultan, Abū Ya’qūb Yūsuf I, and became one of his military advisers. His family then relocated from Murcia to Seville.

ibn ‘Arabī’s dogmatic and intellectual training began in Seville, then the cultural and civilized center of Muslim Iberia, in 578 AH. Most of his teachers were the clergy of the Almohad era and some of them also held the official posts of Qadi or Khatib. He was a young boy when his father sent him to the renowned jurist Abū Bakr ibn Khalaf to study the Qur'an. ibn ‘Arabī learned the recitation of the Qur'an from the book of Al-Kafi in the seven different Qira'at. The same work was also transmitted to him by another ‘Abd al-Raḥmān ibn Ghālib ibn al-Sharrāt. At the age of ten, he was well-versed in the Qira’āt; afterwards he learned the sciences of Hadith, Fiqh and Sirah from the famous scholars of the time such as Al-Suhayli.

Pierre Vogel (b. July 20, 1978 in Frechen), Islamic name Abu Hamza is a German Islamic preacher and a former professional boxer.

Vogel converted to Islam in 2001 and shortly thereafter began courses on Islamic studies in Germany. For two years he studied Arabic and the Quran at the private school Om Al-Qura in Mecca.^{[citation needed]}

In 2006 he returned to Berlin and started teaching Islam at the Al-Nur-Moschee mosque Neukölln, in universities and even among Christians.^{[citation needed]}

After 66 amateur fights^{[citation needed]} he turned professional at the age of 22, fighting briefly (for two years) as a cruiserweightfor the Sauerland club and was undefeated in seven bouts.

Vogel is married to a Muslim Moroccan woman and is father of three children.

He has been described in one German report as a "radical Muslim".

When he appeared at a Muslim meeting in Ferihegy^[when?], he said that polygamy is legitimate due to the fact that there are more women than men in Germany.