Anas reported Allah's Messenger (ﷺ) 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.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا يُونُسُ بْنُ مُحَمَّدٍ، عَنْ حَمَّادِ بْنِ سَلَمَةَ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " لَمَّا صَوَّرَ اللَّهُ آدَمَ فِي الْجَنَّةِ تَرَكَهُ مَا شَاءَ اللَّهُ أَنْ يَتْرُكَهُ فَجَعَلَ إِبْلِيسُ يُطِيفُ بِهِ يَنْظُرُ مَا هُوَ فَلَمَّا رَآهُ أَجْوَفَ عَرَفَ أَنَّهُ خُلِقَ خَلْقًا لاَ يَتَمَالَكُ " .
sunnah.com