Sahih Muslim | Book 32 | Hadith Number 6319

Narrated by Anas
Anas reported Allah's Messenger (may peace be upon him) as saying: 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.