Sheikh al-Islam, may Allah have mercy on him, said (in Majmu' al-Fatawa): "...And for this reason, the head of Islam is {the testimony that there is no god but Allah}, which includes worshipping Allah alone, and abandoning the worship of all else. This is the general Islam, and Allah accepts no religion other than it from the first and the last..." He also said (in Majmu' al-Fatawa): "...And worshipping Allah alone is the origin of religion, and it is the monotheism with which Allah sent the messengers."

The second: The specific origin of the religion of Islam: This is the religion with which Allah sent our Prophet Muhammad, peace be upon him, specifically. It is what Allah has perfected for us, and with it He has completed His favor upon us, and Allah has chosen it as our religion. It is the religion of Islam. The specific origin of the religion of Islam is to utter the two testimonies. This is the first thing a servant is commanded with in the religion of Islam, and a servant's Islam is not realized except by it, and a servant's Islam is not valid if it is nullified. It is the foundation upon which all legal rulings are built. Allah Almighty said: "So that He may forgive your sins, past and future, and complete His favor upon you and guide you to a straight path." [Surah Al-Fath: 13] And from Ibn Abbas, may Allah be pleased with him, that when the Messenger of Allah, peace be upon him, sent Mu'adh ibn Jabal to Yemen, he said: "You are coming to a people of the Book. So call them to the testimony that there is no god but Allah, and that I am the Messenger of Allah." (Narrated by Bukhari and Muslim).

And from Abu Hurayrah, may Allah be pleased with him, that the Messenger of Allah, peace be upon him, said: "I have been commanded to fight the people until they testify that there is no god but Allah, and believe in me and in what I have brought. When they do that, they will have protected from me their blood and their wealth, except by its right, and their reckoning is with Allah." (Narrated by Muslim).