Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Every one of the people of Hell will see his place in Paradise and will say: 'If only Allah Almighty had guided me too!' So this will be a cause of regret for him." And every one of the people of Paradise will see his place in Hell and will say: "Had Allah Almighty not granted me guidance (I would not have come to Paradise)!" So this will be by way of gratitude on his part.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب أهل الجنة / 18660
Hadith Gradingمحدثین:إسنادہ صحیح
Hadith Takhrij«اخرجه احمد فى المسند (512/2) ، أخرجه مسند أحمد برقم: 10274، وأخرجه المستدرك على الصحيحين برقم: 3681»
In one narration the wording is: No one will enter Hell until he has seen his place in Paradise, had he done good (he would have got that place in Paradise); this will be so that it becomes a regret for him. And no one will enter Paradise until he has seen his place in Hell, had he done evil (he would have been given that place); this will be so that he becomes more grateful. Ahmad recorded all these narrations, and the narrators of the first narration are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب أهل الجنة / 18661