Albert Hourani, the British-Lebanese historian of Islamic history, bases his theorisation of Islam, which he claims is not of divine revelation, largely on three factors that revolve around the questions of prophecy, scripture and culture. This article seeks to refute the said claim, arguing that Hourani's contentions are indefensible. With reference to prophecy, Hourani contends that it was impossible for God to communicate with a human being; rather He manifested himself in a human person, like He did with Jesus (peace be upon him). In the absence of a mediator, such an argument has as its proof of validity only the claim of the person so divinely-manifested. In the case of Muhammad (S.A.W), God sent Gabriel, His archangel, to convey His revelations, thereby making the Qur'an, God's words, concrete proof of Muhammad's prophethood. With reference to the question of scripture, this article argues that the fundamental characteristics of the Qur'an, its language and consistency of messages in the face of tumultuous surroundings belie the contention that it was an adaptation from other religions mainly Christianity and Judaism. As for the absence of a viable Arab culture which therefore made borrowings and adoptions inevitable, the article points out that there was an established culture characterised by diversity, differences, economic activities such as trade and the like, all of which render invalid the notion of a cultural vacuum. This article thus argues that Hourani's contentions are untenable. This article further asserts that any analysis of Islam should be based on its main and essential source, the Qur'an.