Shaykh ‘Abdul-‘Aziz ibn ‘Abdullah ibn Baaz (رحمه الله تعالى ورحمة واسعة) said:

“The foundation of the Deen of Islam is to surrender to Allah (عز وجل) through Tawhid, sincerity, abandoning Shirk, and submitting to Allah by carrying out His commands and giving up His prohibitions. This is the very meaning of Islam itself.”

[Majmoo ‘al-Fataawa Ibn Baaz, Vol.: 6; pg. 8]