It is narrated on the authority of Jabir:
''A man came to the Messenger of Allah peace be upon him and said: Messenger of Allah, what are the two things quite unavoidable? He replied: 'He who dies without associating anyone with Allah would (necessarily) enter Paradise and he who dies associating anything with Allah would enter the (Fire of) Hell'.''
This hadeeth explains what makes it inevitable that a person will enter Paradise if he dies believing in Tawheed, and what makes it inevitable that a person will spend eternity in Hell if he dies believing in shirk. This is a definitive principle that is well-known and well established in Islam.