Abu Huraira reported God’s messenger as saying, “If the believer knew the punishment God has prepared, no one would hope for His paradise; and if the infidel knew the extent of His mercy, no one would despair of attaining His paradise.” (Bukhari and Muslim.)
Hadith Referenceمشكوة المصابيح / كتاب الدعوات / 2367
Hadith Gradingالألبانی:مُتَّفَقٌ عَلَيْهِ | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (6469) و مسلم (2755/23)»