Title: Islam
Content:  believe that Islam is the complete and universal version of a primordial faith that was revealed many times before through prophets such as Adam, Abraham, Moses, and Jesus. Muslims consider the Quran, in Arabic, to be the unaltered and final revelation of God. Like other Abrahamic religions, Islam also teaches a final judgment with the righteous rewarded in paradise and the unrighteous punished in hell. Religious concepts and practices include the Five Pillars of Islam, which are obligatory acts of worship, as well as following Islamic law (sharia), which touches on virtually every aspect of life and society, from banking and welfare to women and the environment. The 
Title: Islamic State
Content:  ISIL is a theocracy, proto-state, and a Salafi jihadist group. ISIL's ideology has been described as being a hybrid of Qutbism, Takfirism,  Salafism,  Salafi jihadism,   Wahhabism,   and Sunni Islamist fundamentalism. Although ISIL claims to adhere to the Salafi theology of Ibn Taymiyyah, it rebels against traditional Salafi interpretations as well as the four Sunni schools of law and anathematizes the majority of Salafis as heretics. ISIL ideologues rarely uphold adherence to Islamic scholarship and law manuals for reference, mostly preferring to derive rulings based on self-interpretation of the Qur'an and Muslim traditions. According to Robert Manne, there is a "general consensus" that the ideology 
Title: Ideology of the Islamic State
Content:  The ideology of the Islamic State (IS, also known as ISIS or Daesh), sometimes called Islamic Statism, has been described as being a hybrid of Salafism, Salafi jihadism, Sunni Islamist fundamentalism, Wahhabism, and Qutbism. Through its official statement of beliefs originally released by its first leader Abu Omar al-Baghdadi in 2007 and subsequently updated since June 2014, ISIL defined its creed as "a middle way between the extremist Kharijites and the lax Murji'ites". Important doctrines of ISIL include its belief that it represents the restoration of the caliphate of early Islam, and that all Muslims are required to pledge allegiance to it; that a "defiled" Islam must be purged of apostasy, often with bloody sectarian killings, that the final Day of Judgment by God is near and will follow the defeat of the army of "Rome" by ISIL; that a strict adherence to following the precepts "established by the Prophet Muhammad and his earliest followers" is necessary, surpassing even that of other Salafi-Jihadi groups.
Title: Islamic State
Content:  statement of beliefs originally released by its first leader Abu Omar al-Baghdadi in 2007 and subsequently updated since June 2014, ISIL defined its own creed as "a middle way between the extremist Kharijites and the lax Murji'ites". ISIL's ideology represents radical Jihadi-Salafi Islam, a strict, puritanical form of Sunni Islam. Muslim organisations like Islamic Networks Group (ING) in America have argued against this interpretation of Islam. ISIL promotes religious violence, and regards Muslims who do not agree with its interpretations as infidels or apostates. According to Hayder al Khoei, ISIL's philosophy is represented by the symbolism in the Black Standard variant of the legendary 
Title: Ideology of the Islamic State
Content:  The ideology of the Islamic State is based on Jihadi-Salafism, "a distinct ideological movement in Sunni Islam", according to Cole Bunzel of the Brookings Institution and Graeme Wood of The Atlantic. According to their works, and ISIL itself, it unites two streams of Islamic thought that are the original Muslim Brotherhood and Salafism, though ISIL regards the modern Muslim Brotherhood and Hamas as traitors and apostates. "We believe that jihad in God's path is an individual obligation, from the fall of al-Andalus until the liberation  of  [all]  Muslim  lands,  and  [that  it  is an individual obligation] in the presence of a pious person or an impious person." British newspaper The Guardian defines the organisation's ideology as "generally viewed as identical to al-Qaida's or the Saudi version of Salafism – adherence to fundamental Islamic tenets." However, the sheer brutality and extreme tendencies of ISIL/ISIS have alienated them from mainstream Salafi-Jihadists. Prominent Salafi-Jihadist ideologues have condemned ISIL/ISIS and wrote treatises against them.
Title: Ideology of the Islamic State
Content:  Proof"), ISIL stated that “it was established upon the same principles as the blessed Najdi da’wah state founded by the followers of the Mujaddid Imam Muhammad ibn Abd al-Wahhab” ISIL aims to return to the early days of Islam, rejecting all innovations in the religion, which it believes corrupts its original spirit. It condemns later caliphates and the Ottoman Empire for deviating from what it calls pure Islam. Following Salafi-Jihadi tradition, ISIL condemns the followers of secular law as disbelievers, putting the current Saudi government in that category. According to The Economist, Saudi Wahhabi practices followed by the group include the establishment of religious police 
Title: Gnosticism
Content:   The Quran, like Gnostic cosmology, makes a sharp distinction between this world and the afterlife. God is commonly thought of as being beyond human comprehension. In some Islamic schools of thought, somehow identifiable with the Gnostic Monad. However, according to Islam and unlike most Gnostic sects, not rejection of this world, but performing good deeds leads to the heaven. And according to the Islamic belief in strict Oneness of God, there was no room for a lower deity; such as the demiurge. According to Islam, both good and evil come from one God, a position especially opposed by the Manichaeans. Ibn al-Muqaffa depicted the Islamic deity as a demonic entity who "fights with humans and boasts about His victories" and "sitting 
Title: Islamic views on slavery
Content:  Islamic views on slavery represent a complex and multifaceted body of Islamic thought, with various Islamic groups or thinkers espousing views on the matter which have been radically different throughout history. Slavery was a mainstay of life in pre-Islamic Arabia and surrounding lands. The Quran and the hadith (sayings of Muhammad) address slavery extensively, assuming its existence as part of society but viewing it as an exceptional condition and restricting its scope. Early Islamic dogma forbade enslavement of free members of Islamic society, including non-Muslims (dhimmis), and set out to regulate and improve the conditions of human bondage. Islamic law regarded as legal slaves only those 
Title: Ideology of the Islamic State
Content:  Author Graeme Wood has noted the importance of the "governing precepts that were embedded in Islam by the Prophet Muhammad and his earliest followers" (which together with two succeeding generations of Muslims are known as the Salaf), from which ISIL insists it "cannot waver". "Virtually every major decision and law promulgated by the Islamic State adheres to what it calls, in its press and pronouncements, and on its billboards, license plates, stationery, and coins, 'the Prophetic methodology,' which means following the prophecy and example of Muhammad, in punctilious detail." While other jihadis are salafist in doctrine, ISIL been more exacting in following early practices by "embrac[ing] slavery and crucifixion without apology," as well as a jizya tax on Christians. It has boasted about its enslavement of Yazidi women in its international magazine Dabiq. Despite this, ISIL/ISIS rejects many traditional Salafi interpretations and condemns the majority of Salafis as heretics. Major Salafi scholars of contemporary era such as Saleh Al-Fawzan, Abd Al-Aziz Fawzan Al-Fawzan, Abdulaziz al-Tarefe, Sulaiman Al-Alwan, Adnan al-Aroor, Muhammad Al-Munajjid, etc have refuted the Caliphate claim of ISIL/ISIS as illegal and condemned them as a "rogue, criminal organisation" reminiscent of the "fanatical Kharijites".
Title: Ideology of the Islamic State
Content:  authorities, coupled with absence of major manuals of law for reference led ISIL ideologues to derive personal rulings based on self-interpretation of Qur'an and Traditions. ISIL does not differentiate between Sufis and Salafis in their anathemization. Although ISIL claims to be Salafi they condemn majority of Salafis and despite adopting a Jihadist worldview, they condemn majority of Jihadists. Major scholars of the contemporary Wahhabi movement such as Saleh Al-Fawzan, Abd Al-Aziz Fawzan Al-Fawzan, Abdulaziz al-Tarefe, Sulaiman Al-Alwan, Adnan al-Aroor, Muhammad Al-Munajjid, etc have refuted the Caliphate claim of ISIL as illegal and condemned them as a "rogue, criminal organisation" reminiscent of the "fanatical Kharijites".

Question: what did the islamic people believe in?
Answer: Zakāt.