When Allah fashioned Adam in Paradise, He left him as He liked him to leave. Then Iblis roamed round him to see what actually that was and when he found him hollow from within, he recognised that he had been created with a disposition that he would not have control over himself.
Reference: Sahih Muslim 2611 a In-book : Book 45, Hadith 146 USC-MSA web (English) : Book 32, Hadith 6319 (deprecated)
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