What is the proof that the proper belief is a condition for the acceptance of good deeds? 

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In Suratun-Nisa’, Ayah 124 means, “Those who do deeds of righteousness, be they male or female and are believers, shall enter Paradise and will never be presented with a spec of injustice.” The Prophet, sallallahu ^alayhi wa sallam, said, “The best of the deeds is the belief in Allah and His Messenger.” (Related by al-Bukhariyy.)