The Messenger of Allah ﷺ said, "Every inhabitant of the Fire will see his seat in Paradise and say, 'If only Allah had guided me,' and this will become a source of regret for him. And every inhabitant of Paradise will see his seat in the Fire and say, 'Had Allah not guided me,' and this will become a cause for gratitude on his part."
قال رسول الله ﷺ: كل أهل النار يرى مقعده من الجنة، فيقول: لو أن الله هداني. فيكون عليه حسرة. قال: وكل أهل الجنة يرى مقعده من النار، فيقول: لولا أن الله هداني. قال: فيكون له شكرا.
Reported by Ahmad (10652), and this is his wording, Nasai in Kubra (11390), and Hakim (2/435–436), all of them through the route of Abu Bakr bin Ayyash, from Amash, from Abu Salih, from Abu Hurairah, who said, then he narrated it. Hakim added, then the Messenger of Allah ﷺ recited, "lest a soul should say, 'Alas for me for what I neglected in regard to Allah, and I was indeed among those who mocked,' or say, 'If only Allah had guided me, I would have been among the righteous'" [Zumar 39:56–57].Its chain is hasan because of Abu Bakr bin Ayyash, for his hadith is hasan. Hakim said, "This is a sahih hadith meeting the standard of the two sheikhs."