Ibn Taymiyyah, may Allah have mercy on him, said (in Majmu' al-Fatawa): "Islam is built upon two foundations: realizing the testimony that there is no god but Allah, and that Muhammad is the Messenger of Allah..." He also said, may Allah have mercy on him (in Majmu' al-Fatawa): "...And since the foundation of religion is faith in Allah and His Messenger..."

From the above, it becomes clear: 1. That the foundation of the religion of Islam is the monotheism of Allah Almighty and worshipping Him alone, without associating any partners with Him, and not associating anything with Him, and believing in His Messenger Muhammad, peace and blessings be upon him, and in what he brought from Allah Almighty. 2. That the meaning of "There is no god but Allah" is to believe in the divinity of Allah alone, and to disbelieve in the divinity of anyone other than Him, and to worship Allah alone without partners, and to avoid worshipping others. 3. That nothing enters into the foundation of religion other than the two testimonies. Whoever introduces any other legal ruling into them has gone astray and innovated in the religion of Allah.

Ibn Taymiyyah, may Allah have mercy on him, said (in Dar' al-Ta'arud): "...If people needed in the fundamentals of their religion something that Allah and His Messenger had not explained, then Allah would not have completed their religion for the Ummah, nor would He have completed His favors upon them. We know that every truth that people need in the fundamentals of their religion must be something that the Messenger explained, as the branches of religion cannot stand without their fundamentals. So how is it permissible for the Messenger to leave the fundamentals of religion, without which faith is not complete, without explaining them to the people?! From here, the misguidance of those who innovate a path or belief, claiming that faith is not complete without it, while knowing that the Messenger did not mention it, is understood..." His words concluded, may Allah have mercy on him.