The Messenger of Allah ﷺ said, "Every person of the Fire will see the place he would have occupied in Paradise and will say, 'If only Allah had guided me!' This will become a source of regret for them.And every person of Paradise will see the place he would have occupied in the Fire and will say, 'Had Allah not guided me!' This will become a means of gratitude for him."
حدثنا أسود أخبرنا أبو بكر عن الأعمش عن أبي صالح
قال رسول الله ﷺ كل أهل النار يرى مقعده من الجنة فيقول لو أن الله هداني فيكون عليهم حسرة قال وكل أهل الجنة يرى مقعده من النار فيقول لولا أن الله هداني قال فيكون له شكرا
Its isnad is sahih. Bukhari narrated it, 6/317, no. 3240, in Fath al-Bari, in the Beginning of Creation, chapter on what has been said about the description of Paradise. Muslim narrated it, 4/2199, no. 2866, in Paradise, chapter on the presentation of the deceased's seat in Paradise. Ibn Majah narrated it, 2/1427, no. 4270.