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Hadith Quotes on Beliefs in Islam
Prophet Muhammad peace be upon him stressed the importance of belief over good deeds:
Prophet Muhammad said, "Gabriel said to me, 'Whoever amongst your followers dies and hasn't worshipped any other than Allah, they will enter Paradise (or will not enter Hell)." Prophet Muhammad asked Gabriel: "Even if he has committed illegal sexual intercourse or theft?" and Gabriel replied, "Even then."
Bukhari Volume 4, Book 54, Number 445: Narrated by Abu Dhar