Basics- What is Islaam? [Revisiting and Revising Basics]
In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
What is Islaam? It is to submit to Allaah by worshipping Him alone. Therefore, whoever refuses to submit to Allaah is haughty, and whoever submits to Allaah and others [by devoting any act worship to Allaah and others], then he is guilty of being one who ascribes a partner to Allaah. So, through this it is known that Islam opposes two affairs: Haughtiness and Polytheism [or ascribing partners with Allaah in worship].
Islaam is built on five pillars and the noble Prophet [peace and blessings of Allaah be upon him] has clarified them in the hadeeth reported by Ibn Umar [may Allaah be pleased with him and his father] that the Prophet [peace and blessings of Allaah be upon him] said, “Islaam is built on five pillars: to testify that none has the right to be worshipped except Allaah, establish the prayer [i.e. the five obligatory prayers], pay the Zakaat, fast during the month of Ramadaan and perform Hajj”. [Al-Bukhaari 8 and Muslim 16]
[Source: Explanation of Important Lessons For The Muslim Ummah. pages 41-42. Maktabah Malik Al-Fahad 1436AH. (2015)]