Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates this statement of the Prophet (peace and blessings be upon him): "If a believing servant were to know the punishment present with Allah Almighty, then no one would hope for Paradise; and if a disbelieving person were to know the mercy of Allah Almighty, then no one would despair of Paradise."
Hadith Referenceصحیح ابن حبان / كتاب الرقائق / 656
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الصحيحة» (1634): ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم.